EP0126696B1 - Method for continuously producing an overaged steel strip coated with zinc or an aluminium-zinc alloy - Google Patents

Method for continuously producing an overaged steel strip coated with zinc or an aluminium-zinc alloy Download PDF

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Publication number
EP0126696B1
EP0126696B1 EP84401067A EP84401067A EP0126696B1 EP 0126696 B1 EP0126696 B1 EP 0126696B1 EP 84401067 A EP84401067 A EP 84401067A EP 84401067 A EP84401067 A EP 84401067A EP 0126696 B1 EP0126696 B1 EP 0126696B1
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EP
European Patent Office
Prior art keywords
coating
temperature
band
zinc
over
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Expired
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EP84401067A
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German (de)
French (fr)
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EP0126696A1 (en
EP0126696B2 (en
Inventor
Charles Brun
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USINOR SA
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Union Siderurgique du Nord et de lEst de France SA USINOR
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Priority to AT84401067T priority Critical patent/ATE30744T1/en
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    • 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • 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

Definitions

  • the present invention relates to a method and an installation for the continuous production of a coating of zinc, aluminum or a zinc-aluminum alloy on a steel strip obtained by cold rolling.
  • the invention relates in particular, but not exclusively, to a process for galvanizing a cold-rolled steel strip.
  • the metal cold worked by cold rolling in the form of a strip is first of all subjected to a continuous annealing treatment.
  • This treatment includes a thermal cycle of heating and maintaining temperature, followed by more or less rapid cooling stopped at the melting temperature of the zinc bath.
  • the steel strip is galvanized by dipping in a zinc bath at a temperature between about 460 and 500 ° C., then the strip is continuously extracted from the zinc and cooled before being stored in coils.
  • the metal is completely recrystallized, but the carbon dissolved during the heating and maintenance period of the annealing treatment remains in the state of supersaturated solution in the ferrite. If, at this stage, the cooling of the coated steel strip is continued to a temperature below 270 ° C, at a speed greater than 5 ° C per second, part of the carbon remains in solution.
  • the carbon in supersaturated solution in the ferrite makes the metal sensitive to aging by precipitation of the supersaturated carbon on the dislocations due to the cold deformation that the sheet will subsequently undergo.
  • the supersaturation carbon is precipitated by prolonged annealing in coils.
  • the annealing must be carried out at a temperature below 300 ° C. and must be long, both to obtain sufficient homogeneity of the temperature and complete precipitation of carbon.
  • this result is achieved after maintaining for 6 hours at a temperature above 250 ° C.
  • the surface hardening operation which eliminates the elastic bearing and imprints a roughness set on the surface of the sheet can then be carried out on the metal having undergone such over-aging, without risk of subsequent aging.
  • an overaging cycle which cannot be carried out continuously, is expensive and lengthens the production cycle.
  • FR-A-2 450 285 there is known a method of manufacturing a steel strip coated by immersion in a metal bath, comprising a brutal cooling step downstream of the coating by dipping in the bath, before the overaging treatment .
  • US-A-2,570,906 describes a method and a device for coating a metal strip, in which the coated strip passes through a heat treatment enclosure containing alternating guide rollers.
  • the present invention aims to remedy the aforementioned drawbacks in order to provide a coated sheet which can be continuously processed and have the required technical qualities.
  • the subject of the invention is therefore a continuous process of coating with a layer of Zn, AI or a Zn-AI alloy of a cold rolled steel strip, comprising a thermal heating cycle, followed by a rapid cooling, a dip coating in the molten coating metal bath, at a temperature of 460 to 500 ° C, and subsequent cooling, characterized in that rapid cooling at the end of the heating thermal cycle, the holding temperature at the coating bath temperature, is carried out at a speed of 10 to 50 ° C./s., and that after the dip coating, the coated steel strip is subjected to an overaging treatment by holding tape at a temperature between 430 and 270 ° C for at least two minutes.
  • the rapid cooling following the heating thermal cycle must be carried out at a speed of 10 to 25 ° C / s.
  • the overaging treatment is carried out between 430 and 330 ° C by presenting the same face of the strip in contact with the guide rollers following a spiral path.
  • the steel strip subjected to the overaging treatment is coated on one or both sides with a layer of zinc, aluminum or their alloys.
  • the guide rollers are arranged in such a way so that they are in contact with the free face of the coating layer.
  • the present invention also relates to an installation for continuously coating a layer of Zn, AI or a Zn-AI alloy of a cold-rolled steel strip comprising means for feeding the strip, a heat treatment chamber comprising heating means followed by cooling means, a crucible for keeping the coating metal in fusion, in which are means for returning the strip and means for extracting and guiding the strip and, after the extraction means, an over-aging enclosure, this enclosure comprising a set of guide rollers, characterized in that the guide rollers are arranged so that, during a first path of the strip, only one face of this the latter is in contact with the guide rollers.
  • the guide rollers determine in the first path a spiral winding, then then a second accordion path to the exit of the enclosure.
  • a steel strip cold worked by cold rolling is first of all subjected to a continuous annealing treatment in the galvanizing line according to a thermal cycle which is illustrated in FIG. 1.
  • the overaging treatment can be considerably shortened if it is carried out after rapid cooling of the metal before entering the zinc bath.
  • Complete overaging can be achieved by holding for at least 2 minutes at about 430-270 ° C, provided that the rapid cooling rate from about 800 ° C to about 470 ° C is preferably greater than 10 ° C / s.
  • One of the original characteristics of the process of the present invention consists in minimizing this risk by an arrangement of the guide rollers relative to the strip, so that only one face of the strip, in the portion where the strip is at higher temperature. at 330 ° C or in contact with the guide rollers. This completely avoids the risk of scratches for the side not in contact with the guide rollers in the part where the strip is at a temperature above 330 ° C.
  • the face thus preserved from contact with the guide rollers will be reserved as a visible face, in particular in body sheets which must have a perfect surface condition.
  • the thermal cycle undergone by the steel strip has been represented, representing, on the one hand, the aging according to the present invention and, on the other hand, normal cooling of the strip without aging .
  • the method of the present invention is implemented in an installation partially shown in FIG. 1.
  • the strip 1 of cold rolled steel is supplied from supply means not shown in an oven 2, where it undergoes an annealing treatment with a heating phase in zone 3 and cooling in zone 4.
  • the strip 1 is then continuously galvanized by dipping in a bath of molten zinc 5 contained in a crucible 6.
  • This crucible is provided with means for returning the strip in the form of a roller 7 immersed in the bath zinc.
  • Tape 1 is then extracted vertically from the zinc bath 5 and undergoes conventional treatment operations for the layer of zinc deposited in zones 8 and is guided by a roller 9 in the direction of the overaging enclosure 10.
  • the steel strip carrying its zinc coating is introduced into the overaging enclosure 10 through an orifice 11 at a temperature close to this location of 370 ° C.
  • the overaging enclosure 10 includes a set of guide rollers arranged horizontally and parallel to each other.
  • the strip 1 travels in this enclosure a first path from its entry 11 passing over the guide rollers 12, 13, 14, 15 and 16 according to a spiral winding, so that the same face of this strip from its exit from the bath zinc is in contact with the guide rollers.
  • the temperature of the strip is approximately 330 ° C., so that it is then possible to put the face which has not undergone any contact with the guide rollers with these.
  • the strip follows an accordion path on the rollers 17 and 18a to 18d, as well as 19a to 19c, the rollers 18a to 18d being arranged respectively at the upper part of the enclosure, while the rollers 19a to 19c are arranged at the lower part of the latter.
  • the strip is extracted from the enclosure 10 through an orifice 20 at a temperature of 270 ° C. and sent using suitable rollers to a work hardening station, not shown, after cooling to a temperature - at 50 ° vs.
  • the temperature of the enclosure is regulated so as to ensure a strip temperature of at least 370 ° C. at the inlet of the enclosure and at least 270 ° C. at the outlet of the enclosure.
  • the length of the aging zone is provided in such a way that the effective time between leaving the zinc bath and leaving the aging zone at a temperature greater than or equal to 270 ° C. is at least 2 minutes and, from preferably between 2 and 5 minutes approximately for the galvanization of steel intended to be stamped.
  • the strip of galvanized steel ends up at the end of a hardening rolling mill, not shown, so as to erase the elastic flow bearing and to impart a surface roughness adjusted to the sheet, then the strip is wound up and stored.
  • guide rollers of the overaging enclosure must have a diameter such that the diameter to thickness ratio of the strip is greater than 800, so as to avoid hardening the metal by work hardening.
  • the guide rollers are in particular hollow rolls of steel with rectified surface, having a fine roughness (0.5 wm), burnished by oxidation between 300 and 500 ° C.
  • the face comprising the thin coating of iron-zinc alloy is presented in contact with the guide rollers 9 and 12 to 15 of the overaging treatment zone. This keeps the conventional zinc coating out of contact with the guide rollers during the first spiral wound path. As the face comprising the thin coating of iron-zinc alloy is not subject to deterioration in contact with the guide rollers, there is no deterioration in its qualities.
  • Cycle 1 corresponds to the prior art without overaging treatment with continuous hardening at the end of the line of 1%.
  • Cycle 2 corresponds to galvanizing according to the prior art with over-aging in a coil not allowing continuous treatment.
  • the reappearance of the elastic bearing is, moreover, relatively low compared to cycle 1 not comprising an overaging step.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Thermal Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Coating With Molten Metal (AREA)
  • Heat Treatment Of Strip Materials And Filament Materials (AREA)
  • Belt Conveyors (AREA)
  • Heat Treatment Of Articles (AREA)
  • Heat Treatments In General, Especially Conveying And Cooling (AREA)

Abstract

The present invention relates to a continuous coating process by a layer of Zn, Al or of a Zn-Al alloy for a cold laminated steel band comprising a heating thermic cycle, followed by a rapid cooling, a tempered coating in the metal bath of coating in fusion, at a temperature from 460 DEG to 500 DEG C., and a subsequent cooling, characterized in that after the tempered coating, the coated steel band is subjected to an over-ageing treatment by maintaining the band at a temperature comprised between 430 DEG and 270 DEG C. during at least two minutes. This process is carried out in an installation comprising an over-ageing chamber.

Description

La présente invention est relative à un procédé et une installation pour la réalisation en continu d'un revêtement de zinc, d'aluminium ou d'un alliage zinc-aluminium sur une bande d'acier obtenue par laminage à froid.The present invention relates to a method and an installation for the continuous production of a coating of zinc, aluminum or a zinc-aluminum alloy on a steel strip obtained by cold rolling.

L'invention vise en particulier, mais non exclusivement, un procédé de galvanisation d'une bande d'acier laminée à froid.The invention relates in particular, but not exclusively, to a process for galvanizing a cold-rolled steel strip.

Dans les procédés classiques de galvanisation actuellement exploités, le métal écroui par laminage à froid se présentant sous forme d'une bande est tout d'abord soumis à un traitement de recuit en continu. Ce traitement comporte un cycle thermique de chauffage et de maintien à température, suivi d'un refroidissement plus ou moins rapide arrêté à la température de fusion du bain de zinc. Après le traitement de recuit, suivi du refroidissement plus ou moins rapide, la bande d'acier est galvanisée au trempé dans un bain de zinc à une température comprise entre environ 460 et 500 °C, puis la bande est extraite en continu du bain de zinc et refroidie avant d'être stockée en bobines.In the conventional galvanizing processes currently used, the metal cold worked by cold rolling in the form of a strip is first of all subjected to a continuous annealing treatment. This treatment includes a thermal cycle of heating and maintaining temperature, followed by more or less rapid cooling stopped at the melting temperature of the zinc bath. After the annealing treatment, followed by more or less rapid cooling, the steel strip is galvanized by dipping in a zinc bath at a temperature between about 460 and 500 ° C., then the strip is continuously extracted from the zinc and cooled before being stored in coils.

On effectue sur le revêtement de zinc issu du bain liquide diverses opérations afin de lui conférer les propriétés désirées.Various operations are carried out on the zinc coating obtained from the liquid bath in order to give it the desired properties.

A la sortie du bain de zinc, le métal est totalement recristallisé, mais le carbone mis en solution au cours de la période de chauffage et de maintien du traitement de recuit reste à l'état de solution sursaturée dans la ferrite. Si, à ce stade, le refroidissement de la bande d'acier revêtue est poursuivi jusqu'à une température inférieure à 270 °C, à une vitesse supérieure à 5 °C par seconde, une partie du carbone reste en solution. Le carbone en solution sursaturée dans la ferrite rend le métal sensible au vieillissement par précipitation du carbone en sursaturation sur les dislocations dues à la déformation à froid que subira ultérieurement la tôle.At the exit from the zinc bath, the metal is completely recrystallized, but the carbon dissolved during the heating and maintenance period of the annealing treatment remains in the state of supersaturated solution in the ferrite. If, at this stage, the cooling of the coated steel strip is continued to a temperature below 270 ° C, at a speed greater than 5 ° C per second, part of the carbon remains in solution. The carbon in supersaturated solution in the ferrite makes the metal sensitive to aging by precipitation of the supersaturated carbon on the dislocations due to the cold deformation that the sheet will subsequently undergo.

Le vieillissement qui a lieu dans les deux mois suivant la déformation ne permet pas d'effectuer la passe d'écrouissage de surface sur la ligne de galvanisation, car les caractéristiques mécaniques d'un acier traité dans ces conditions serait instable dans le temps. En effet, le durcissement dû au vieillissement s'accompagne d'une réapparition du palier d'écoulement élastique supprimé par la passe d'écrouissage de surface et, en conséquence, au cours de la mise en oeuvre ultérieure, le métal présentera des défauts de conformation (facettes) ou des défauts de surface en creux (vermiculures) dus à une répartition non uniforme et aléatoire de la déformation plastique.Aging which takes place within two months of deformation does not allow the surface hardening pass to be carried out on the galvanizing line, since the mechanical characteristics of a steel treated under these conditions would be unstable over time. Indeed, hardening due to aging is accompanied by a reappearance of the elastic flow bearing suppressed by the surface hardening pass and, consequently, during the subsequent processing, the metal will exhibit defects of conformation (facets) or hollow surface defects (vermiculures) due to a non-uniform and random distribution of the plastic deformation.

Selon la technique actuellement mise en oeuvre, pour éviter ce type de défauts dus au vieillissement, on précipite le carbone en sursaturation par un recuit prolongé en bobines. Pour éviter de transformer le revêtement de zinc présent sur la bande d'acier en alliage fer-zinc fragile, le recuit doit être effectué à une température inférieure à 300 °C et doit être long, à la fois pour obtenir une homogénéité suffisante de la température et une précipitation complète du carbone. L'expérience montre que ce résultat est atteint après un maintien de 6 heures à température supérieure à 250 °C.According to the technique currently used, to avoid this type of defects due to aging, the supersaturation carbon is precipitated by prolonged annealing in coils. To avoid transforming the zinc coating present on the steel strip into a fragile iron-zinc alloy, the annealing must be carried out at a temperature below 300 ° C. and must be long, both to obtain sufficient homogeneity of the temperature and complete precipitation of carbon. Experience shows that this result is achieved after maintaining for 6 hours at a temperature above 250 ° C.

L'opération d'écrouissage de surface qui élimine le palier élastique et imprime une rugosité réglée à la surface de la tôle peut être effectuée ensuite sur le métal ayant subi un tel survieillissement, sans risque de vieillissement ultérieur. Cependant, un tel cycle de survieillissement, qui ne peut être effectué en continu, est coûteux et allonge le cycle de production.The surface hardening operation which eliminates the elastic bearing and imprints a roughness set on the surface of the sheet can then be carried out on the metal having undergone such over-aging, without risk of subsequent aging. However, such an overaging cycle, which cannot be carried out continuously, is expensive and lengthens the production cycle.

Selon FR-A-2 450 285 on connaît un procédé de fabrication d'une bande d'acier revêtue par immersion dans un bain métallique, comportant une étape de refroidissement brutal en aval du revêtement au trempé dans le bain, avant le traitement de survieillissement.According to FR-A-2 450 285 there is known a method of manufacturing a steel strip coated by immersion in a metal bath, comprising a brutal cooling step downstream of the coating by dipping in the bath, before the overaging treatment .

US-A-2 570 906 décrit un procédé et un dispositif de revêtement d'une bande métallique, dans lequel la bande revêtue passe dans une enceinte de traitement thermique contenant des rouleaux de guidage alternés.US-A-2,570,906 describes a method and a device for coating a metal strip, in which the coated strip passes through a heat treatment enclosure containing alternating guide rollers.

La présente invention a pour but de remédier aux inconvénients précités afin de fournir une tôle revêtue qui puisse être traitée en continu et posséder les qualités techniques requises.The present invention aims to remedy the aforementioned drawbacks in order to provide a coated sheet which can be continuously processed and have the required technical qualities.

L'invention a ainsi pour objet un procédé en continu de revêtement par une couche de Zn, AI ou d'un alliage Zn-AI d'une bande d'acier laminée à froid, comprenant un cycle thermique de chauffage, suivi d'un refroidissement rapide, un revêtement au trempé dans le bain de métal de revêtement en fusion, à une température de 460 à 500 °C, et un refroidissement ultérieur, caractérisé en ce que le refroidissement rapide à la fin du cycle thermique de chauffage, de la température de maintien à la température du bain de revêtement, est réalisé à une vitesse de 10 à 50°C/s., et qu'après le revêtement au trempé, la bande d'acier revêtue est soumise à un traitement de survieillissement par maintien de la bande à une température comprise entre 430 et 270 °C pendant au moins deux minutes.The subject of the invention is therefore a continuous process of coating with a layer of Zn, AI or a Zn-AI alloy of a cold rolled steel strip, comprising a thermal heating cycle, followed by a rapid cooling, a dip coating in the molten coating metal bath, at a temperature of 460 to 500 ° C, and subsequent cooling, characterized in that rapid cooling at the end of the heating thermal cycle, the holding temperature at the coating bath temperature, is carried out at a speed of 10 to 50 ° C./s., and that after the dip coating, the coated steel strip is subjected to an overaging treatment by holding tape at a temperature between 430 and 270 ° C for at least two minutes.

Selon une caractéristique de ce procédé, le refroidissement rapide à la suite du cycle thermique de chauffage doit être effectué à une vitesse de 10 à 25 °C/s.According to a characteristic of this process, the rapid cooling following the heating thermal cycle must be carried out at a speed of 10 to 25 ° C / s.

Selon une autre caractéristique de la présente invention, le traitement de survieillissement est effectué entre 430 et 330 °C en présentant la même face de la bande en contact avec les rouleaux de guidage suivant un trajet en colimaçon.According to another characteristic of the present invention, the overaging treatment is carried out between 430 and 330 ° C by presenting the same face of the strip in contact with the guide rollers following a spiral path.

La bande d'acier soumise au traitement de survieillissement est revêtue sur une ou ses deux faces d'une couche de zinc, d'aluminium ou de leurs alliages. Dans le cas où la bande ne comporte un revêtement d'épaisseur classique que sur une de ses faces, on dispose les rouleaux de guidage de telle sorte qu'ils soient en contact avec la face exempte de la couche de revêtement.The steel strip subjected to the overaging treatment is coated on one or both sides with a layer of zinc, aluminum or their alloys. In the case where the strip only has a coating of conventional thickness on one of its faces, the guide rollers are arranged in such a way so that they are in contact with the free face of the coating layer.

La présente invention a également pour objet une installation de revêtement en continu d'une couche de Zn, AI ou d'un alliage Zn-AI d'une bande d'acier laminée à froid comportant des moyens d'alimentation de la bande, une enceinte de traitement thermique comportant des moyens de chauffage suivis de moyens de refroidissement, un creuset de maintien en fusion du métal de revêtement dans lequel sont disposés des moyens de renvoi de la bande et des moyens d'extraction et de guidage de la bande et, après les moyens d'extraction, une enceinte de survieillissement, cette enceinte comportant un ensemble de rouleaux de guidage, caractérisé en ce que les rouleaux de guidage sont disposés de telle sorte que, pendant un premier trajet de la bande, seule une face de cette dernière soit en contact avec les rouleaux de guidage.The present invention also relates to an installation for continuously coating a layer of Zn, AI or a Zn-AI alloy of a cold-rolled steel strip comprising means for feeding the strip, a heat treatment chamber comprising heating means followed by cooling means, a crucible for keeping the coating metal in fusion, in which are means for returning the strip and means for extracting and guiding the strip and, after the extraction means, an over-aging enclosure, this enclosure comprising a set of guide rollers, characterized in that the guide rollers are arranged so that, during a first path of the strip, only one face of this the latter is in contact with the guide rollers.

Selon une autre caractéristique, les rouleaux de guidage déterminent dans le premier trajet un enroulement en colimaçon, puis ensuite un second trajet en accordéon jusqu'à la sortie de l'enceinte.According to another characteristic, the guide rollers determine in the first path a spiral winding, then then a second accordion path to the exit of the enclosure.

L'invention est exposée ci-après plus en détail à l'aide des dessins annexés, qui en représentent seulement un mode de réalisation.The invention is set out below in more detail with the aid of the appended drawings, which show only one embodiment.

Sur ces dessins :

  • la figure 1 est un schéma illustrant le cycle thermique suivi par la bande au cours de la galvanisation en continu ;
  • la figure 2 est une vue schématique partielle d'une installation de revêtement en continu selon la présente invention dans sa partie comportant l'enceinte de survieillissement.
In these drawings:
  • Figure 1 is a diagram illustrating the thermal cycle followed by the strip during continuous galvanization;
  • Figure 2 is a partial schematic view of a continuous coating installation according to the present invention in its part comprising the overaging enclosure.

L'invention sera décrite ci-après en référence à un procédé de galvanisation en continu, mais cette technique peut également s'appliquer à l'aluminisation ou au revêtement d'un alliage zinc-aluminium.The invention will be described below with reference to a continuous galvanizing process, but this technique can also be applied to the aluminizing or coating of a zinc-aluminum alloy.

Une bande d'acier écrouie par laminage à froid est tout d'abord soumise à un traitement de recuit en continu dans la ligne de galvanisation suivant un cycle thermique qui est illustré à la figure 1.A steel strip cold worked by cold rolling is first of all subjected to a continuous annealing treatment in the galvanizing line according to a thermal cycle which is illustrated in FIG. 1.

Ce cycle thermique comporte :

  • - une phase de chauffage très rapide jusqu'à une température comprise entre 550 et 750 °C environ, la vitesse de chauffage étant comprise entre 20 et 200 °C/s. environ ;
  • - une phase de chauffage plus lent jusqu'à la température de maintien comprise entre 650 et 850 °C environ, la vitesse de chauffage étant comprise entre 5 et 50 °C/s. ;
  • - une phase de maintien à température comprise entre 650 et 850 °C d'une durée allant de 20 secondes à 3 minutes environ ;
  • - un refroidissement rapide de la température de maintien à la température d'entrée dans le bain de zinc en fusion qui est à une température comprise entre 460 et 500 °C, la vitesse de refroidissement étant de 10 à 50 °C/s ;
  • - une galvanisation au trempé vers 450 °C dans un bain de zinc pendant un temps compris entre 1 et 10 secondes environ ;
  • - une poursuite du refroidissement de la bande revêtue de zinc comportant un traitement de survieillissement en continu sur la ligne de galvanisation qui sera détaillé ci-après.
This thermal cycle includes:
  • - a very rapid heating phase up to a temperature of between 550 and 750 ° C approximately, the heating rate being between 20 and 200 ° C / s. about ;
  • - A slower heating phase up to the holding temperature of between 650 and 850 ° C approximately, the heating rate being between 5 and 50 ° C / s. ;
  • - a temperature maintenance phase between 650 and 850 ° C lasting from 20 seconds to 3 minutes approximately;
  • - Rapid cooling from the holding temperature to the entry temperature into the molten zinc bath which is at a temperature between 460 and 500 ° C, the cooling rate being from 10 to 50 ° C / s;
  • - dip galvanization at around 450 ° C in a zinc bath for a time of between 1 and 10 seconds approximately;
  • - further cooling of the zinc-coated strip comprising a continuous overaging treatment on the galvanizing line which will be detailed below.

Le traitement de survieillissement peut être considérablement raccourci s'il est effectué après un refroidissement rapide du métal avant l'entrée dans le bain de zinc. Un survieillissement complet peut être obtenu par maintien pendant au moins 2 minutes entre 430 et 270 °C environ, à condition que la vitesse de refroidissement rapide de 800 °C environ à 470 °C environ soit de préférence supérieure à 10 °C/s.The overaging treatment can be considerably shortened if it is carried out after rapid cooling of the metal before entering the zinc bath. Complete overaging can be achieved by holding for at least 2 minutes at about 430-270 ° C, provided that the rapid cooling rate from about 800 ° C to about 470 ° C is preferably greater than 10 ° C / s.

La réalisation d'un tel cycle pour un produit galvanisé présente cependant l'inconvénient de devoir maintenir pendant un temps prolongé le zinc à une température supérieure à 330 °C, ce qui accroît le risque de collage et de grippage du revêtement de zinc au contact des rouleaux de guidage de la ligne.However, carrying out such a cycle for a galvanized product has the drawback of having to maintain the zinc for a long time at a temperature above 330 ° C., which increases the risk of sticking and seizing of the zinc coating on contact. line guide rollers.

Une des caractéristiques originales du procédé de la présente invention consiste à minimiser ce risque par une disposition des rouleaux de guidage par rapport à la bande, de telle sorte qu'une seule face de la bande, dans la portion où la bande est à température supérieure à 330 °C soit en contact avec les rouleaux de guidage. On évite ainsi totalement le risque de griffes pour la face non en contact avec les rouleaux de guidage dans la partie où la bande est à une température supérieure à 330 °C.One of the original characteristics of the process of the present invention consists in minimizing this risk by an arrangement of the guide rollers relative to the strip, so that only one face of the strip, in the portion where the strip is at higher temperature. at 330 ° C or in contact with the guide rollers. This completely avoids the risk of scratches for the side not in contact with the guide rollers in the part where the strip is at a temperature above 330 ° C.

La face ainsi préservée du contact avec les rouleaux de guidage sera réservée comme face visible, notamment dans les tôles de carrosserie devant présenter un état de surface parfait.The face thus preserved from contact with the guide rollers will be reserved as a visible face, in particular in body sheets which must have a perfect surface condition.

Sur le schéma de la figure 1, on a représenté le cycle thermique subi par la bande d'acier en représentant, d'une part, le survieillissement selon la présente invention et, d'autre part, un refroidissement normal de la bande sans survieillissement.In the diagram of FIG. 1, the thermal cycle undergone by the steel strip has been represented, representing, on the one hand, the aging according to the present invention and, on the other hand, normal cooling of the strip without aging .

Le procédé de la présente invention est mis en oeuvre dans une installation représentée partiellement à la figure 1.The method of the present invention is implemented in an installation partially shown in FIG. 1.

Sur cette figure 1, la bande 1 d'acier laminé à froid est alimentée à partir de moyens d'alimentation non représentés dans un four 2, où elle subit un traitement de recuit avec une phase de chauffage dans la zone 3 et de refroidissement dans la zone 4. La bande 1 est ensuite galvanisée en continu au trempé dans un bain de zinc en fusion 5 contenu dans un creuset 6. Ce creuset est muni de moyens de renvoi de la bande sous forme d'un rouleau 7 immergé dans le bain de zinc. La bande 1 est ensuite extraite verticalement du bain de zinc 5 et subit des opérations de traitement classiques de la couche de zinc déposée dans des zones 8 et est guidée par un rouleau 9 en direction de l'enceinte de survieillissement 10. La bande d'acier portant son revêtement de zinc est introduite dans l'enceinte de survieillissement 10 par un orifice 11 à une température voisine à cet endroit de 370 °C. L'enceinte de survieillissement 10 comporte un ensemble de rouleaux de guidage disposés horizontalement et parallèlement les uns aux autres. La bande 1 parcourt dans cette enceinte un premier trajet depuis son entrée 11 en passant sur les rouleaux de guidage 12,13,14,15 et 16 suivant un enroulement en colimaçon, de sorte que la même face de cette bande depuis sa sortie du bain de zinc soit en contact avec les rouleaux de guidage. Lorsqu'elle parvient au niveau du rouleau de guidage 16, la température de la bande est d'environ 330 °C, de sorte qu'il soit alors possible de mettre la face n'ayant subi aucun contact avec les rouleaux de guidage en contact avec ces derniers. A partir du rouleau 16, la bande poursuit un trajet en accordéon sur les rouleaux 17 et 18a à 18d, ainsi que 19a à 19c, les rouleaux 18a à 18d étant disposés respectivement à la partie supérieure de l'enceinte, alors que les rouleaux 19a à 19c sont disposés à la partie inférieure de cette dernière. La bande est extraite de l'enceinte 10 par un orifice 20 à une température de 270 °C et envoyée à l'aide de rouleaux appropriés vers un poste d'écrouissage non représenté, après refroidissement jusqu'à une température -- à 50 °C.In this FIG. 1, the strip 1 of cold rolled steel is supplied from supply means not shown in an oven 2, where it undergoes an annealing treatment with a heating phase in zone 3 and cooling in zone 4. The strip 1 is then continuously galvanized by dipping in a bath of molten zinc 5 contained in a crucible 6. This crucible is provided with means for returning the strip in the form of a roller 7 immersed in the bath zinc. Tape 1 is then extracted vertically from the zinc bath 5 and undergoes conventional treatment operations for the layer of zinc deposited in zones 8 and is guided by a roller 9 in the direction of the overaging enclosure 10. The steel strip carrying its zinc coating is introduced into the overaging enclosure 10 through an orifice 11 at a temperature close to this location of 370 ° C. The overaging enclosure 10 includes a set of guide rollers arranged horizontally and parallel to each other. The strip 1 travels in this enclosure a first path from its entry 11 passing over the guide rollers 12, 13, 14, 15 and 16 according to a spiral winding, so that the same face of this strip from its exit from the bath zinc is in contact with the guide rollers. When it reaches the level of the guide roller 16, the temperature of the strip is approximately 330 ° C., so that it is then possible to put the face which has not undergone any contact with the guide rollers with these. From the roller 16, the strip follows an accordion path on the rollers 17 and 18a to 18d, as well as 19a to 19c, the rollers 18a to 18d being arranged respectively at the upper part of the enclosure, while the rollers 19a to 19c are arranged at the lower part of the latter. The strip is extracted from the enclosure 10 through an orifice 20 at a temperature of 270 ° C. and sent using suitable rollers to a work hardening station, not shown, after cooling to a temperature - at 50 ° vs.

La température de l'enceinte est régulée de façon à assurer une température de bande de 370 °C au moins à l'entrée de l'enceinte et de 270 °C au moins à la sortie de l'enceinte.The temperature of the enclosure is regulated so as to ensure a strip temperature of at least 370 ° C. at the inlet of the enclosure and at least 270 ° C. at the outlet of the enclosure.

La longueur de la zone de survieillissement est prévue de telle manière que le temps effectif entre la sortie du bain de zinc et la sortie de la zone de survieillissement à température supérieure ou égale à 270 °C soit d'au moins 2 minutes et, de préférence, comprise entre 2 et 5 minutes environ pour la galvanisation d'acier destiné à être embouti.The length of the aging zone is provided in such a way that the effective time between leaving the zinc bath and leaving the aging zone at a temperature greater than or equal to 270 ° C. is at least 2 minutes and, from preferably between 2 and 5 minutes approximately for the galvanization of steel intended to be stamped.

La bande d'acier galvanisé parvient en bout de ligne à un laminoir écrouisseur non représenté, de façon à effacer le palier d'écoulement élastique et à imprimer une rugosité de surface réglée à la tôle, puis la bande est enroulée et stockée.The strip of galvanized steel ends up at the end of a hardening rolling mill, not shown, so as to erase the elastic flow bearing and to impart a surface roughness adjusted to the sheet, then the strip is wound up and stored.

Une caractéristique importante des rouleaux de guidage de l'enceinte de survieillissement est qu'ils doivent présenter un diamètre tel que le rapport diamètre sur épaisseur de la bande soit supérieur à 800, de façon à éviter de durcir le métal par écrouissage.An important characteristic of the guide rollers of the overaging enclosure is that they must have a diameter such that the diameter to thickness ratio of the strip is greater than 800, so as to avoid hardening the metal by work hardening.

Les rouleaux de guidage sont notamment des rouleaux creux en acier à surface rectifiée, ayant une rugosité fine (0,5 wm), brunie par oxidation entre 300 et 500 °C.The guide rollers are in particular hollow rolls of steel with rectified surface, having a fine roughness (0.5 wm), burnished by oxidation between 300 and 500 ° C.

Un traitement d'oxydation effectué sur les rouleaux de guidage de la zone de survieillissement et auto-entretenu par l'oxydation atmosphérique, crée une couche qui s'oppose au collage ou au grippage de la bande à condition que la rugosité des rouleaux soit inférieure à 0,5 µm.An oxidation treatment carried out on the guide rollers of the overaging zone and self-maintained by atmospheric oxidation, creates a layer which opposes the sticking or seizing of the strip provided that the roughness of the rollers is less at 0.5 µm.

Dans le cas où la bande d'acier galvanisé présente sur une de ses faces un revêtement de zinc d'épaisseur classique et sur l'autre face un mince revêtement d'alliage fer-zinc obtenu par élimination de la couche de zinc préalablement déposée, on présente la face comportant le mince revêtement d'alliage fer-zinc en contact avec les rouleaux de guidage 9 et 12 à 15 de la zone de traitement de survieillissement. Ceci permet de maintenir le revêtement classique de zinc hors du contact avec les rouleaux de guidage pendant le premier trajet enroulé en colimaçon. La face comportant le mince revêtement d'alliage fer-zinc n'étant pas sujette à détérioration au contact des rouleaux de guidage, on n'observe aucune détérioration de ses qualités.In the case where the strip of galvanized steel has on one side a coating of zinc of conventional thickness and on the other side a thin coating of iron-zinc alloy obtained by elimination of the layer of zinc previously deposited, the face comprising the thin coating of iron-zinc alloy is presented in contact with the guide rollers 9 and 12 to 15 of the overaging treatment zone. This keeps the conventional zinc coating out of contact with the guide rollers during the first spiral wound path. As the face comprising the thin coating of iron-zinc alloy is not subject to deterioration in contact with the guide rollers, there is no deterioration in its qualities.

Afin de mettre en évidence les caractéristiques avantageuses obtenues par le procédé de la présente invention, on effectue trois cycles de galvanisation définis ci-après.In order to highlight the advantageous characteristics obtained by the process of the present invention, three galvanization cycles defined below are carried out.

Le cycle 1 correspond à la technique antérieure sans traitement de survieillissement avec un écrouissage en continu en bout de ligne de 1 %.Cycle 1 corresponds to the prior art without overaging treatment with continuous hardening at the end of the line of 1%.

Le cycle 2 correspond à une galvanisation selon la technique antérieure avec un survieillissement en bobine ne permettant pas un traitement en continu.Cycle 2 corresponds to galvanizing according to the prior art with over-aging in a coil not allowing continuous treatment.

Le cycle 3 correspond au procédé de la présente invention.

  • Cycle 1
    • Galvanisation en continu à 820 °C
    • Refroidissement de 820 à 470 °C à 10 °C/s. de 430 à 270 °C à 5 °C/s.
    • Ecrouissage 1 % en ligne.
  • Cycle 2
    • Galvanisation en continu à 820 °C
    • Refroidissement de 820 à 470 °C à 10 °C/s. de 430 à 270 °C à 5 °C/s.
    • Survieillissement 6 heures à 280 °C
    • Ecrouissage 1 %.
  • Cycle 3
    • Galvanisation en continu à 820 °C
    • Refroidissement de 820 à 470 °C à 10 °C/s. de 430 à 270 °C à 0,8 °C/s.
    • (survieillissement)
    • Ecrouissage 1 % en ligne.
Cycle 3 corresponds to the process of the present invention.
  • Cycle 1
    • Continuous galvanization at 820 ° C
    • Cooling from 820 to 470 ° C to 10 ° C / s. from 430 to 270 ° C at 5 ° C / s.
    • 1% work hardening online.
  • Cycle 2
    • Continuous galvanization at 820 ° C
    • Cooling from 820 to 470 ° C to 10 ° C / s. from 430 to 270 ° C at 5 ° C / s.
    • 6 hours over aging at 280 ° C
    • Work hardening 1%.
  • Cycle 3
    • Continuous galvanization at 820 ° C
    • Cooling from 820 to 470 ° C to 10 ° C / s. from 430 to 270 ° C at 0.8 ° C / s.
    • (aging)
    • 1% work hardening online.

Les caractéristiques mécaniques du produit obtenu après écrouissage dans les divers cycles sont données au tableau suivant, tout d'abord dans l'état de livraison à la sortie des lignes et, ensuite, après deux mois de stockage à 30 °C.

Figure imgb0001
The mechanical characteristics of the product obtained after work hardening in the various cycles are given in the following table, firstly in the state of delivery at the outlet of the lines and, then, after two months of storage at 30 ° C.
Figure imgb0001

On peut constater à la lecture de ce tableau que dans le cycle 3 selon la présente invention, l'accroissement de la limite élastique est faible après deux mois de stockage et tout à fait comparable à celui obtenu pour le cycle 2 ne permettant pas une galvanisation en continu totale sur toute la ligne.It can be seen from reading this table that in cycle 3 according to the present invention, the increase in the elastic limit is small after two months of storage and quite comparable to that obtained for cycle 2 which does not allow galvanizing. continuously continuous across the line.

La réapparition du palier élastique est, par ailleurs, relativement faible par rapport au cycle 1 ne comportant pas d'étape de survieillissement.The reappearance of the elastic bearing is, moreover, relatively low compared to cycle 1 not comprising an overaging step.

Claims (9)

1. Continuous process for coating a cold lamined steel band with a layer of Zn, AI or with a Zn-Al alloy, comprising a heating thermic cycle, followed by rapid cooling, a tempered coating in the metal bath of coating in fusion at a temperature of 460 to 500 °C, and a subsequent cooling, characterised in that the rapid cooling at the end of the heating thermic cycle, from the maintenance temperature to the coating bath temperature, is accomplished at a speed from 10 to 50 °C/s. and that after the tempered coating, the coated steel band is subjected to an over-ageing treatment by maintaining the band at a temperature between 430 and 270 °C for at least two minutes.
2. Process according to claim 1, characterized in that the heating thermic cycle comprises a very rapid rise in temperature until a temperature comprised between 550 and 750 °C at a speed of 20 to 200 °C/s., slower continued rise in temperature until a maintenance temperature comprised between 650 and 850 °C at a speed of 5 to 50 °C/s. and maintaining this temperature for about 20 seconds to 3 minutes, followed by rapid cooling at a speed of 10 to 50 °C/s of from the maintenance temperature to the coating bath temperature.
3. Process according to claim 1, characterized in that the rapid cooling speed is from 10 to 25 °C/s.
4. Process according to claim 1, characterized in that the over-ageing treatment is accomplished between 430 and 330 °C by presenting the same face of the band in contact with the guiding rolls according to a helix travel path.
5. Process according to any one of the preceding claims, characterized in that the coated band being subjected to the over-ageing treatment comprises in this over-ageing zone a face coated with a conventional zinc-coating and a face coated with a thin iron-zinc alloy layer which is put in contact with the guiding rolls.
6. Continuous coating installation of a layer of Zn, AI or of a Zn-Al alloy for a cold laminated steel band (1) comprising feeding means for the band, a thermic treatment chamber (2) comprising heating means (3), followed by cooling means (4), a crucible (6) for maintaining in fusion the coating metal in which the return means (7) of the band (1) are disposed and extraction and guiding means of the band, after the extraction means, an over-ageing chamber (10), this chamber comprising an assembly of guiding rolls (12 to 19) characterized in that the guiding rolls (12 to 19) arranged in such a manner that, during the first travel path of the band, only one face of the latter is in contact with the guiding rolls.
7. Installation according to claim 6, characterized in that the guiding rolls determine in the first travel path an helix winding, and then a second accordion travel path up to the exit from the chamber.
8. Installation according to claim 6, characterized in that the guiding rolls of the over-ageing chamber have a diameter such that the ratio roll diameter/thickness of the band is higher than 800.
9. Installation according to any one of claims 6 to 8, characterized in that the steel guiding rolls comprise an oxide coating.
EP84401067A 1983-05-24 1984-05-23 Method for continuously producing an overaged steel strip coated with zinc or an aluminium-zinc alloy Expired - Lifetime EP0126696B2 (en)

Priority Applications (1)

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AT84401067T ATE30744T1 (en) 1983-05-24 1984-05-23 METHOD AND DEVICE FOR CONTINUOUS PRODUCTION OF AGED STEEL STRIP COATED WITH ALUMINIUM, ZINC OR WITH AN ALUMINUM-ZINC ALLOY.

Applications Claiming Priority (2)

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FR8308508A FR2546534B1 (en) 1983-05-24 1983-05-24 PROCESS AND INSTALLATION FOR THE CONTINUOUS MANUFACTURE OF A STRIP OF OLD STEEL CARRYING A COATING OF ZN, AL OR ZN-AL ALLOY
FR8308508 1983-05-24

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DE19822156A1 (en) * 1998-05-16 1999-11-18 Schloemann Siemag Ag Method and device for performing the annealing of a galvannealing process
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AU3057884A (en) 1986-01-16
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EP0126696A1 (en) 1984-11-28
FR2546534B1 (en) 1989-04-21
CA1215889A (en) 1986-12-30
JPS6052529A (en) 1985-03-25
EP0126696B2 (en) 1992-02-19
ES8801711A1 (en) 1988-02-16
ATE30744T1 (en) 1987-11-15
AU569094B2 (en) 1988-01-21
ES541797A0 (en) 1988-02-16
US4620501A (en) 1986-11-04
US4530858A (en) 1985-07-23
ES533091A0 (en) 1985-10-16
FR2546534A1 (en) 1984-11-30

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