EP0577584A1 - Method of protecting a hot rolled steel product - Google Patents

Method of protecting a hot rolled steel product Download PDF

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Publication number
EP0577584A1
EP0577584A1 EP93870121A EP93870121A EP0577584A1 EP 0577584 A1 EP0577584 A1 EP 0577584A1 EP 93870121 A EP93870121 A EP 93870121A EP 93870121 A EP93870121 A EP 93870121A EP 0577584 A1 EP0577584 A1 EP 0577584A1
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EP
European Patent Office
Prior art keywords
product
temperature
deposited
coating
metallic coating
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Application number
EP93870121A
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German (de)
French (fr)
Inventor
Yves Hardy
Jean-François Noville
Pierre Simon
Stéphan Wilmotte
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Centre de Recherches Metallurgiques CRM ASBL
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Centre de Recherches Metallurgiques CRM ASBL
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Publication of EP0577584A1 publication Critical patent/EP0577584A1/en
Withdrawn legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/68—Temporary coatings or embedding materials applied before or during heat treatment
    • C21D1/70—Temporary coatings or embedding materials applied before or during heat treatment while heating or quenching
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B45/00—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/02—Hardening articles or materials formed by forging or rolling, with no further heating beyond that required for the formation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/38—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling sheets of limited length, e.g. folded sheets, superimposed sheets, pack rolling
    • B21B2001/383—Cladded or coated products
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching

Definitions

  • the present invention relates to a method for protecting a hot-rolled steel product.
  • steel products Upon leaving the hot rolling mill, steel products are generally at a temperature of the order of 1000 ° C., at which they have an entirely austenitic structure.
  • the hot-rolled products are then cooled to room temperature, according to procedures intended to give them a set of desired mechanical properties.
  • the hot products are brought into contact with a cooling agent, generally water or air; this contact causes the formation, on the surface of the product, of a thin layer of scale, essentially consisting of adherent iron oxide.
  • a cooling agent generally water or air; this contact causes the formation, on the surface of the product, of a thin layer of scale, essentially consisting of adherent iron oxide.
  • cold steel products can be exposed to various atmospheres, for example humid or saline, which promote their corrosion.
  • Some of these substances such as paints or oils, must be applied to cooled products; it is then generally necessary to clean the surface of the products, for example by pickling, to remove surface oxides and restore sufficient adhesion.
  • metallic substances such as zinc or certain zinc alloys could offer interesting protection for steel products, not only during their storage but also during their use. These metals, however, have a serious handicap, since their adhesion, and therefore their effectiveness, largely depends on their conditions of application.
  • the object of the present invention is to provide a method for protecting a hot-rolled steel product by applying a coating of zinc or a zinc alloy during a particular procedure for cooling this product. at the exit of the hot rolling mill.
  • the cooling procedure referred to above is currently known in the art by its acronym "QST", that is to say “Quenching and Self-Tempering” or “Quenching and Self-Income”. It basically consists of three stages.
  • the first step consists in subjecting the hot product, which leaves the rolling mill, to abrupt and short-term surface cooling, such as it causes in the product the formation of a surface layer of martensite or bainite, that is to say ie a quenching structure.
  • This first cooling is generally carried out with cold water.
  • the surface of the product is at a temperature below the point M s of the steel used, while the internal part of the product is not reached by sudden cooling.
  • the product is then subjected, in a second step, to natural cooling in the air which results in an equalization of the temperature in the section of the product; the surface heats up by transferring heat from the internal part, while this internal part cools slowly.
  • the surface layer of martensite or bainite undergoes tempering, while in the internal part the initial austenite begins to transform into ferrite and carbides.
  • the equalization temperature is generally between 400 ° C and 700 ° C.
  • the product finally cools down substantially homogeneously throughout its section, to room temperature, with further processing of the austenite of the internal parts into ferrite and carbides. This latter cooling is the third step in this known procedure.
  • the present invention makes it possible to take advantage of the particular conditions which this process presents for ensuring effective protection of hot-rolled steel products.
  • the steel products considered here essentially include long products, such as bars, beams, rails, profiles of various shapes, and so-called small iron products.
  • the invention also relates to a steel product having improved corrosion protection, obtained by applying the present method.
  • a process for protecting a hot-rolled steel product comprising a first step which consists of a surface quenching of the product from the end of rolling temperature, a second step which consists of a stay in the air with temperature equalization in the section of the product and self-tempering of the hardened surface layer, and a third step which consists of a final cooling of the product in the air from from the equalization temperature to room temperature, is characterized in that a metal coating is deposited on the surface of the product during the temperature equalization phase during said second step.
  • the equalization of the temperature in the section of the product simultaneously comprises, on the one hand, the heating of the surface layer from the end of quenching temperature to the equalization temperature and on the other hand, the continuous cooling of the internal part of the product to the equalization temperature.
  • the equalization temperature is the temperature reached at each point in the product section at the time when the heat exchanges balance at this point.
  • this equalization temperature is not necessarily reached at the same instant in all the points of the section, in particular because of the complexity of the heat exchanges resulting from the geometry of the section of the product. It can therefore happen that there is a temperature difference between the surface and the interior of the product, when this surface reaches its equalization temperature. This possible temperature difference plays no role in the process of the invention, which relates to a coating operation involving only the surface of the product.
  • the equalization temperature to be considered here is the maximum temperature reached by the surface of the product during the second stage of treatment.
  • the moment when the surface of the product reaches its maximum temperature marks the separation between the second and third stages of the treatment.
  • the metallic coating can be deposited at any time during this warming phase. However, it has been found to be advantageous to carry out this deposition when the surface temperature is below 400 ° C., and is preferably between 150 ° C. and 300 ° C. It has in fact been found, unexpectedly, that the adhesion of the metallic coating on the product was better when the temperature of the surface is within the limits indicated.
  • the metal coating can be removed by any suitable method. It is however preferably deposited by projection, in particular because this technique does not require a bulky or sophisticated installation.
  • the protection of steel products can be achieved by means of various metals or metal alloys, preferably chosen from so-called low melting metals or alloys.
  • the protective coating can also be made of a zinc alloy containing between 1% and 8%, and preferably about 4% of aluminum.
  • This alloy has a particularly high adhesion, thanks to the formation of a layer of intermetallic compounds of the Fe-Al-Zn type, during self-tempering.
  • a metallic coating is thus formed on the steel product, the thickness of which is between 5 ⁇ m and 30 ⁇ m.
  • This thickness is sufficient to provide the desired protection during the rest of the heat treatment, in particular during the final cooling, as well as during subsequent storage.
  • This metallic coating can also be completed by depositing a second layer of metal or metal alloy on the product during the final cooling.
  • This additional coating is preferably deposited, also by spraying, when the temperature of the product is, at least on the surface, below 400 ° C.
  • the thickness of this additional coating is such that the final coating has a total thickness of 25 ⁇ m to 150 ⁇ m.
  • This additional coating is particularly recommended for steel products intended to undergo numerous manipulations or to be exposed for long periods in aggressive atmospheres such as marine or industrial atmospheres.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Coating With Molten Metal (AREA)
  • Heat Treatments In General, Especially Conveying And Cooling (AREA)

Abstract

A hot-rolled iron or steel product (rod, section) is subjected to a continuous quenching and self-annealing heat treatment. A metal coating (Zn; Zn-Al) is deposited on the surface of the product during the temperature-equalising stage, preferably when the surface of the product is at a temperature lower than 400 DEG C. An additional metal coating may be deposited on the product during its final cooling, preferably when its temperature is lower than 400 DEG C. The thickness of the first coating is between 5 mu m and 30 mu m; the total thickness is between 25 mu m and 150 mu m.

Description

La présente invention concerne un procédé de protection d'un produit sidérurgique laminé à chaud.The present invention relates to a method for protecting a hot-rolled steel product.

A leur sortie du laminoir à chaud, les produits sidérurgiques se trouvent généralement à une température de l'ordre de 1000°C, à laquelle ils présentent une structure entièrement austénitique. Les produits laminés à chaud sont ensuite refroidis jusqu'à la température ambiante, suivant des procédures destinées à leur conférer un ensemble de propriétés mécaniques désirées.Upon leaving the hot rolling mill, steel products are generally at a temperature of the order of 1000 ° C., at which they have an entirely austenitic structure. The hot-rolled products are then cooled to room temperature, according to procedures intended to give them a set of desired mechanical properties.

Pour assurer ce refroidissement, les produits chauds sont mis en contact avec un agent réfrigérant, généralement l'eau ou l'air; ce contact provoque la formation, à la surface du produit, d'une mince couche de calamine, essentiellement constituée d'oxyde de fer adhérent.To ensure this cooling, the hot products are brought into contact with a cooling agent, generally water or air; this contact causes the formation, on the surface of the product, of a thin layer of scale, essentially consisting of adherent iron oxide.

Ultérieurement, lors d'un stockage avant d'être utilisés, les produits sidérurgiques froids peuvent être exposés à diverses atmosphères, par exemple humides ou salines, qui favorisent leur corrosion.Subsequently, during storage before being used, cold steel products can be exposed to various atmospheres, for example humid or saline, which promote their corrosion.

Pour éviter de compromettre leur mise en oeuvre, il est souvent recommandé d'assurer la protection de ces produits aussi tôt que possible après leur sortie du laminoir à chaud.To avoid compromising their implementation, it is often recommended to ensure the protection of these products as soon as possible after they leave the hot rolling mill.

Parmi les nombreuses méthodes qui ont été proposées jusqu'à présent pour assurer cette protection, on peut citer le dépôt de différentes substances telles que certaines poudres d'oxydes, des peintures, des huiles, des phosphates, des métaux ou des alliages métalliques.Among the numerous methods which have been proposed up to now for ensuring this protection, mention may be made of the deposition of different substances such as certain oxide powders, paints, oils, phosphates, metals or metal alloys.

Certaines de ces substances, comme les peintures ou les huiles, doivent être appliquées sur les produits refroidis; il est alors généralement nécessaire de nettoyer la surface des produits, par exemple par décapage, pour éliminer les oxydes superficiels et rétablir une adhérence suffisante.Some of these substances, such as paints or oils, must be applied to cooled products; it is then generally necessary to clean the surface of the products, for example by pickling, to remove surface oxides and restore sufficient adhesion.

D'autres substances, telles que les poudres d'oxydes, peuvent être appliquées à haute température mais doivent être éliminées avant la mise en oeuvre des produits.Other substances, such as oxide powders, can be applied at high temperature but must be removed before using the products.

D'autres encore, en particulier les phosphates et les substances analogues, requièrent que la surface des produits soit propre pour permettre la réaction chimique des phosphates avec cette surface.Still others, especially phosphates and the like, require that the surface of the products be clean to allow the chemical reaction of the phosphates with that surface.

Enfin, les substances métalliques telles que le zinc ou certains alliages de zinc pourraient offrir une protection intéressante des produits sidérurgiques, non seulement au cours de leur stockage mais également lors de leur mise en oeuvre. Ces métaux présentent cependant un grave handicap, du fait que leur adhérence, et par conséquent leur efficacité, dépend largement de leurs conditions d'application.Finally, metallic substances such as zinc or certain zinc alloys could offer interesting protection for steel products, not only during their storage but also during their use. These metals, however, have a serious handicap, since their adhesion, and therefore their effectiveness, largely depends on their conditions of application.

La présente invention a pour objet de proposer un procédé de protection d'un produit sidérurgique laminé à chaud, par l'application d'un revêtement de zinc ou d'un alliage de zinc au cours d'une procédure particulière de refroidissement de ce produit à la sortie du laminoir à chaud.The object of the present invention is to provide a method for protecting a hot-rolled steel product by applying a coating of zinc or a zinc alloy during a particular procedure for cooling this product. at the exit of the hot rolling mill.

La procédure de refroidissement à laquelle il est fait référence ci-dessus est actuellement connue dans la technique par son sigle "QST", c'est-à-dire "Quenching and Self-Tempering" ou encore "Trempe et Auto-Revenu". Elle comprend essentiellement trois étapes. La première étape consiste à soumettre le produit chaud, qui quitte le laminoir, à un refroidissement superficiel brusque et de courte durée, tel qu'il provoque dans le produit la formation d'une couche superficielle de martensite ou de bainite, c'est-à-dire d'une structure de trempe. Ce premier refroidissement est généralement réalisé à l'eau froide. A la fin de cette première étape, la surface du produit se trouve à une température inférieure au point Ms de l'acier utilisé, tandis que la partie interne du produit n'est pas atteinte par le refroidissement brusque. Le produit est ensuite soumis, au cours d'une deuxième étape, à un refroidissement naturel dans l'air qui se traduit par une égalisation de la température dans la section du produit; la surface se réchauffe par transfert de la chaleur venant de la partie interne, tandis que cette partie interne se refroidit lentement. De ce fait, la couche superficielle de martensite ou de bainite subit un revenu, tandis que, dans la partie interne, l'austénite initiale commence à se transformer en ferrite et en carbures. La température d'égalisation s'établit généralement entre 400°C et 700°C. Le produit se refroidit enfin de façon sensiblement homogène dans toute sa section, jusqu'à la température ambiante, avec poursuite de la transformation de l'austénite des parties internes en ferrite et en carbures. Ce dernier refroidissement constitue la troisième étape de cette procédure connue.The cooling procedure referred to above is currently known in the art by its acronym "QST", that is to say "Quenching and Self-Tempering" or "Quenching and Self-Income". It basically consists of three stages. The first step consists in subjecting the hot product, which leaves the rolling mill, to abrupt and short-term surface cooling, such as it causes in the product the formation of a surface layer of martensite or bainite, that is to say ie a quenching structure. This first cooling is generally carried out with cold water. At the end of this first step, the surface of the product is at a temperature below the point M s of the steel used, while the internal part of the product is not reached by sudden cooling. The product is then subjected, in a second step, to natural cooling in the air which results in an equalization of the temperature in the section of the product; the surface heats up by transferring heat from the internal part, while this internal part cools slowly. As a result, the surface layer of martensite or bainite undergoes tempering, while in the internal part the initial austenite begins to transform into ferrite and carbides. The equalization temperature is generally between 400 ° C and 700 ° C. The product finally cools down substantially homogeneously throughout its section, to room temperature, with further processing of the austenite of the internal parts into ferrite and carbides. This latter cooling is the third step in this known procedure.

La présente invention permet de profiter des conditions particulières que présente ce procédé pour assurer une protection efficace des produits sidérurgiques laminés à chaud.The present invention makes it possible to take advantage of the particular conditions which this process presents for ensuring effective protection of hot-rolled steel products.

A ce propos, il convient d'indiquer que les produits sidérurgiques considérés ici comprennent essentiellement les produits longs, tels que les barres, les poutrelles, les rails, les profilés de formes diverses, et les produits dits petits fers.In this regard, it should be noted that the steel products considered here essentially include long products, such as bars, beams, rails, profiles of various shapes, and so-called small iron products.

L'invention porte également sur un produit sidérurgique présentant une protection améliorée contre la corrosion, obtenu par l'application du présent procédé.The invention also relates to a steel product having improved corrosion protection, obtained by applying the present method.

Conformément à la présente invention, un procédé de protection d'un produit sidérurgique laminé à chaud, ledit produit étant soumis à un traitement thermique continu comprenant une première étape qui consiste en une trempe superficielle du produit à partir de la température de fin de laminage, une deuxième étape qui consiste en un séjour dans l'air avec égalisation de la température dans la section du produit et auto-revenu de la couche superficielle trempée, et une troisième étape qui consiste en un refroidissement final du produit dans l'air à partir de la température d'égalisation jusqu'à la température ambiante, est caractérisé en ce que l'on dépose un revêtement métallique sur la surface du produit pendant la phase d'égalisation de la température au cours de ladite deuxième étape.In accordance with the present invention, a process for protecting a hot-rolled steel product, said product being subjected to a continuous heat treatment comprising a first step which consists of a surface quenching of the product from the end of rolling temperature, a second step which consists of a stay in the air with temperature equalization in the section of the product and self-tempering of the hardened surface layer, and a third step which consists of a final cooling of the product in the air from from the equalization temperature to room temperature, is characterized in that a metal coating is deposited on the surface of the product during the temperature equalization phase during said second step.

Comme on l'a indiqué plus haut, l'égalisation de la température dans la section du produit comprend simultanément d'une part le réchauffement de la couche superficielle depuis la température de fin de trempe jusqu'à la température d'égalisation et d'autre part le refroidissement continu de la partie interne du produit jusqu'à la température d'égalisation.As indicated above, the equalization of the temperature in the section of the product simultaneously comprises, on the one hand, the heating of the surface layer from the end of quenching temperature to the equalization temperature and on the other hand, the continuous cooling of the internal part of the product to the equalization temperature.

En principe, la température d'égalisation est la température atteinte en chaque point de la section du produit à l'instant où les échanges thermiques s'équilibrent en ce point.In principle, the equalization temperature is the temperature reached at each point in the product section at the time when the heat exchanges balance at this point.

Dans la pratique cependant, cette température d'égalisation n'est pas nécessairement atteinte au même instant dans tous les points de la section, notamment en raison de la complexité des échanges thermiques résultant de la géométrie de la section du produit. Il peut donc arriver qu'il subsiste un écart de température entre la surface et l'intérieur du produit, au moment où cette surface atteint sa température d'égalisation. Cet éventuel écart de température ne joue aucun rôle dans le procédé de l'invention, qui concerne une opération de revêtement intéressant uniquement la surface du produit.In practice, however, this equalization temperature is not necessarily reached at the same instant in all the points of the section, in particular because of the complexity of the heat exchanges resulting from the geometry of the section of the product. It can therefore happen that there is a temperature difference between the surface and the interior of the product, when this surface reaches its equalization temperature. This possible temperature difference plays no role in the process of the invention, which relates to a coating operation involving only the surface of the product.

De ce fait, la température d'égalisation à considérer ici est la température maximale atteinte par la surface du produit pendant la deuxième étape du traitement. En pratique, l'instant où la surface du produit atteint sa température maximale marque la séparation entre la deuxième et la troisième étape du traitement.Therefore, the equalization temperature to be considered here is the maximum temperature reached by the surface of the product during the second stage of treatment. In practice, the moment when the surface of the product reaches its maximum temperature marks the separation between the second and third stages of the treatment.

Il en résulte que le dépôt d'un revêtement métallique sur la surface du produit, conformément à l'invention, est effectué pendant la phase de réchauffement de la surface du produit entre la température de fin de trempe et la température d'égalisation de cette surface.It follows that the deposition of a metallic coating on the surface of the product, in accordance with the invention, is carried out during the phase of reheating of the surface of the product between the end of quenching temperature and the equalization temperature of this product. area.

Le dépôt du revêtement métallique peut être effectué à un moment quelconque de cette phase de réchauffement. Il s'est cependant avéré intéressant d'effectuer ce dépôt alors que la température de la surface est inférieure à 400°C, et est de préférence comprise entre 150°C et 300°C. On a en effet constaté, de manière inattendue, que l'adhérence du revêtement métallique sur le produit était meilleure lorsque la température de la surface est comprise dans les limites indiquées.The metallic coating can be deposited at any time during this warming phase. However, it has been found to be advantageous to carry out this deposition when the surface temperature is below 400 ° C., and is preferably between 150 ° C. and 300 ° C. It has in fact been found, unexpectedly, that the adhesion of the metallic coating on the product was better when the temperature of the surface is within the limits indicated.

Le revêtement métallique peut être déposé par toute méthode appropriée. Il est cependant déposé de préférence par projection, en particulier parce que cette technique ne nécessite pas une installation encombrante ou sophistiquée.The metal coating can be removed by any suitable method. It is however preferably deposited by projection, in particular because this technique does not require a bulky or sophisticated installation.

La protection des produits sidérurgiques peut être réalisée au moyen de divers métaux ou alliages métalliques, choisis de préférence parmi les métaux ou alliages dits à bas point de fusion.The protection of steel products can be achieved by means of various metals or metal alloys, preferably chosen from so-called low melting metals or alloys.

Il est particulièrement intéressant d'utiliser du zinc, ou un alliage à base de zinc, pour réaliser ce revêtement, notamment en raison de la protection sacrificielle qu'il offre en cas d'endommagement du dépôt.It is particularly advantageous to use zinc, or a zinc-based alloy, to produce this coating, in particular because of the sacrificial protection which it offers in the event of damage to the deposit.

Le revêtement protecteur peut encore être réalisé en un alliage de zinc contenant entre 1 % et 8 %, et de préférence environ 4 % d'aluminium. Cet alliage présente une adhérence particulièrement élevée, grâce à la formation d'une couche de composés intermétalliques du type Fe-Al-Zn, au cours de l'auto-revenu.The protective coating can also be made of a zinc alloy containing between 1% and 8%, and preferably about 4% of aluminum. This alloy has a particularly high adhesion, thanks to the formation of a layer of intermetallic compounds of the Fe-Al-Zn type, during self-tempering.

On forme ainsi sur le produit sidérurgique un revêtement métallique dont l'épaisseur est comprise entre 5 µm et 30 µm.A metallic coating is thus formed on the steel product, the thickness of which is between 5 μm and 30 μm.

Cette épaisseur, dont la valeur préférée est de l'ordre de 15 à 20 µm, est suffisante pour assurer la protection désirée pendant la suite du traitement thermique, notamment pendant le refroidissement final, ainsi que pendant le stockage ultérieur.This thickness, the preferred value of which is of the order of 15 to 20 μm, is sufficient to provide the desired protection during the rest of the heat treatment, in particular during the final cooling, as well as during subsequent storage.

On peut encore compléter ce revêtement métallique par le dépôt d'une seconde couche de métal ou d'alliage métallique sur le produit au cours du refroidissement final. Ce revêtement complémentaire est de préférence déposé, également par projection, lorsque la température du produit est, au moins en surface, inférieure à 400°C.This metallic coating can also be completed by depositing a second layer of metal or metal alloy on the product during the final cooling. This additional coating is preferably deposited, also by spraying, when the temperature of the product is, at least on the surface, below 400 ° C.

L'épaisseur de ce revêtement complémentaire est telle que le revêtement final ait une épaisseur totale de 25 µm à 150 µm.The thickness of this additional coating is such that the final coating has a total thickness of 25 μm to 150 μm.

Ce revêtement complémentaire est particulièrement recommandé pour les produits sidérurgiques destinés à subir de nombreuses manipulations ou à être exposés pendant de longues périodes dans des atmosphères agressives telles que des atmosphères marines ou industrielles.This additional coating is particularly recommended for steel products intended to undergo numerous manipulations or to be exposed for long periods in aggressive atmospheres such as marine or industrial atmospheres.

Claims (10)

Procédé de protection d'un produit sidérurgique laminé à chaud, ledit produit étant soumis à un traitement thermique continu comprenant une première étape qui consiste en une trempe superficielle du produit à partir de la température de fin de laminage, une deuxième étape qui consiste en un séjour dans l'air avec égalisation de la température dans la section du produit et auto-revenu de la couche superficielle trempée, et une troisième étape qui consiste en un refroidissement final du produit dans l'air à partir de la température d'égalisation jusqu'à la température ambiante, caractérisé en ce que l'on dépose un revêtement métallique sur la surface du produit pendant la phase d'égalisation de la température au cours de ladite deuxième étape.Method for protecting a hot-rolled steel product, said product being subjected to a continuous heat treatment comprising a first step which consists of a surface quenching of the product from the end of rolling temperature, a second step which consists of a air stay with temperature equalization in the product section and self-tempering of the hardened surface layer, and a third step which consists of a final cooling of the product in the air from the equalization temperature to 'at room temperature, characterized in that a metal coating is deposited on the surface of the product during the temperature equalization phase during said second step. Procédé suivant la revendication 1, caractérisé en ce que l'on dépose ledit revêtement métallique sur ledit produit pendant la partie de ladite phase d'égalisation où la surface du produit se trouve à une température comprise entre la température de fin de trempe superficielle et 400°C.Process according to Claim 1, characterized in that the said metallic coating is deposited on the said product during the part of the said equalization phase where the surface of the product is at a temperature between the end of surface quenching temperature and 400 ° C. Procédé suivant l'une ou l'autre des revendications 1 et 2, caractérisé en ce que l'on dépose ledit revêtement métallique sur ledit produit pendant la partie de ladite phase d'égalisation où la surface du produit se trouve à une température comprise entre 150°C et 300°C.Method according to either of Claims 1 and 2, characterized in that the said metallic coating is deposited on the said product during the part of the said equalization phase where the surface of the product is at a temperature between 150 ° C and 300 ° C. Procédé suivant l'une ou l'autre des revendications 1 à 3, caractérisé en ce que l'on dépose ledit revêtement métallique par projection.Process according to either of Claims 1 to 3, characterized in that the said metallic coating is deposited by projection. Procédé suivant l'une ou l'autre des revendications 1 à 4, caractérisé en ce que l'on dépose un revêtement métallique constitué de zinc ou d'un alliage à base de zinc.Process according to either of Claims 1 to 4, characterized in that a metal coating consisting of zinc or a zinc-based alloy is deposited. Procédé suivant l'une ou l'autre des revendications 1 à 5, caractérisé en ce que l'on dépose un revêtement métallique complémentaire sur le produit au cours du refroidissement final du produit pendant ladite troisième étape du traitement thermique.Process according to either of Claims 1 to 5, characterized in that an additional metallic coating is deposited on the product during the final cooling of the product during said third stage of the heat treatment. Procédé suivant la revendication 6, caractérisé en ce que l'on dépose ledit revêtement métallique complémentaire lorsque la surface dudit produit se trouve à une température inférieure à 400°C.Process according to Claim 6, characterized in that the said complementary metallic coating is deposited when the surface of the said product is at a temperature below 400 ° C. Produit sidérurgique laminé à chaud, pourvu d'un revêtement métallique déposé par le procédé de l'une ou l'autre des revendications précédentes, caractérisé en ce que ledit revêtement est constitué d'un alliage de zinc contenant de 1 % à 8 % d'aluminium.Hot-rolled steel product provided with a metallic coating deposited by the process of either of the preceding claims, characterized in that said coating consists of a zinc alloy containing from 1% to 8% d 'aluminum. Produit sidérurgique suivant la revendication 8, pourvu d'un revêtement métallique déposé par le procédé de l'une ou l'autre des revendications 1 à 5, caractérisé en ce que ledit revêtement présente une épaisseur comprise entre 5 µm et 30 µm.Steel product according to claim 8, provided with a metallic coating deposited by the process of any one of claims 1 to 5, characterized in that said coating has a thickness of between 5 µm and 30 µm. Produit sidérurgique suivant la revendication 8, pourvu d'un revêtement métallique déposé par le procédé de l'une ou l'autre des revendications 6 et 7, caractérisé en ce que ledit revêtement métallique présente une épaisseur totale comprise entre 25 µm et 150 µm.Steel product according to claim 8, provided with a metallic coating deposited by the process of either of claims 6 and 7, characterized in that said metallic coating has a total thickness of between 25 µm and 150 µm.
EP93870121A 1992-06-29 1993-06-28 Method of protecting a hot rolled steel product Withdrawn EP0577584A1 (en)

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BE9200603 1992-06-29
BE9200603A BE1005964A6 (en) 1992-06-29 1992-06-29 Protection method of hot rolled steel product.

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2204693A1 (en) * 1972-10-31 1974-05-24 Centre Rech Metallurgique
BE858862A (en) * 1977-09-19 1978-01-16 Centre Rech Metallurgique PROCESS FOR IMPROVING THE QUALITY OF STEEL PROFILES
DD282246A5 (en) * 1987-09-01 1990-09-05 ������@������������������@���@�������@��������@�K@��K@��k�� METHOD FOR TREATING ROLLING STEEL TO INCREASE CORROSION RESISTANCE

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2204693A1 (en) * 1972-10-31 1974-05-24 Centre Rech Metallurgique
BE858862A (en) * 1977-09-19 1978-01-16 Centre Rech Metallurgique PROCESS FOR IMPROVING THE QUALITY OF STEEL PROFILES
DD282246A5 (en) * 1987-09-01 1990-09-05 ������@������������������@���@�������@��������@�K@��K@��k�� METHOD FOR TREATING ROLLING STEEL TO INCREASE CORROSION RESISTANCE

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