EP1457580A1 - Method for the control of oxidation of sheets before hot dip galvanizing and galvanizing line - Google Patents

Method for the control of oxidation of sheets before hot dip galvanizing and galvanizing line Download PDF

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Publication number
EP1457580A1
EP1457580A1 EP04290508A EP04290508A EP1457580A1 EP 1457580 A1 EP1457580 A1 EP 1457580A1 EP 04290508 A EP04290508 A EP 04290508A EP 04290508 A EP04290508 A EP 04290508A EP 1457580 A1 EP1457580 A1 EP 1457580A1
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EP
European Patent Office
Prior art keywords
strip
galvanizing
temperature
furnace
heating means
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
EP04290508A
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German (de)
French (fr)
Inventor
François Mignard
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Fives Stein SA
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Stein Heurtey SA
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Publication of EP1457580A1 publication Critical patent/EP1457580A1/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
    • 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
    • C21D9/54—Furnaces for treating strips or wire
    • C21D9/56—Continuous furnaces for strip or wire
    • C21D9/561—Continuous furnaces for strip or wire with a controlled atmosphere or vacuum
    • 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
    • C23C2/003—Apparatus
    • C23C2/0034—Details related to elements immersed in bath
    • C23C2/00342—Moving elements, e.g. pumps or mixers
    • C23C2/00344—Means for moving substrates, e.g. immersed rollers or immersed bearings
    • 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
    • C23C2/003—Apparatus
    • C23C2/0035—Means for continuously moving substrate through, into or out of the 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
    • C23C2/003—Apparatus
    • C23C2/0038—Apparatus characterised by the pre-treatment chambers located immediately upstream of the bath or occurring locally before the dipping process
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
    • C23C2/0222—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating in a reactive atmosphere, e.g. oxidising or reducing atmosphere
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
    • C23C2/0224—Two or more thermal pretreatments
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • 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
    • C23C2/06—Zinc or cadmium 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
    • C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
    • C23C2/36—Elongated material
    • C23C2/40—Plates; Strips
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
    • F24H9/00—Details
    • F24H9/0005—Details for water heaters
    • F24H9/0042—Cleaning arrangements
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
    • F25D11/00—Self-contained movable devices, e.g. domestic refrigerators

Definitions

  • the invention relates to a galvanizing process continuously hot by dipping a steel strip having oxidizable additives in one proportion to improve properties steel mechanics.
  • Hot dip galvanizing ovens typically comprise several sections equipped to carry out different phases heat treatment which are generally: heating, holding, cooling.
  • the oven heat treatment is conditioned by an atmosphere neutral or reducing, generally consisting of mixture of nitrogen and hydrogen to reduce iron oxides present on the surface of the front plates their galvanization.
  • the object of the proposed invention is to provide a device and method for hot-dip galvanizing continuously tempered which allow to process correctly bands containing elements of oxidizable addition the content of which is sufficient for improve the mechanical properties of steel.
  • the invention relates to a galvanizing line in continuous hot with the dip of a steel strip having oxidizable additives in one proportion to improve properties steel mechanics, according to which the strip travels in a galvanizing furnace under an atmosphere reducing, with soaking in a galvanizing bath, this line being characterized in that it comprises upstream of the galvanizing furnace a heating means tape at an appropriate temperature followed by area to expose the strip to an oxidizing atmosphere whose oxygen content is such that, taking into account the strip temperature and the duration of the treatment, the oxidizable addition elements of the steel strip be oxidized on the surface and immediately below the surface of the strip before they could not migrate to said surface to form a layer of oxides capable of causing defects in galvanizing.
  • the iron oxides produced during this operation will be reduced during the passage of the tape in the oven.
  • the strip is brought to a temperature between 150 ° C and 400 ° C, preferably between 150 ° C and 300 ° C approximately, for the oxidation treatment.
  • the control of the oxidation of its surface, for an oxidizing atmosphere given will be made by the choice of the couple strip temperature / residence time in the oxidizing atmosphere.
  • Control of this temperature / residence time couple will be carried out continuously and will take into account the operation of the line, in particular the instant tape speed.
  • the control of the tape oxidation treatment can be carried out by regulating the heating power located upstream of the oven (action on the temperature of the band) or by acting on the distance between the element heater located upstream of the oven and the oven inlet (action on the oxidation time).
  • the oxidizing atmosphere in which takes place the controlled oxidation operation of the surface of the tape can be ambient air or any other atmosphere confined in an enclosure installed upstream of the oven and whose oxygen content will be checked.
  • FIG. 1 of the drawings we can see, schematically shown, a galvanizing line continuously hot by dipping a steel strip 1 in a zinc galvanizing bath in fusion 2.
  • the line includes a galvanizing oven produced according to state of the art 3 for the treatment of strip 1 before its soaking in the bath 2.
  • the oven includes several sections equipped to carry out successively the different phases of the treatment which are generally heating, maintaining then cooling to a temperature suitable for the deposition of zinc on the surface of the strip.
  • the atmosphere of the oven 3 is reducing, produced by a mixture of gases traditionally nitrogen with hydrogen with a dew point kept as low as possible.
  • the steel strip 1 contains addition elements oxidizable such as Si, Cr, Mn, Mo in proportions sufficient to improve its characteristics mechanical.
  • addition elements oxidizable such as Si, Cr, Mn, Mo in proportions sufficient to improve its characteristics mechanical.
  • this type of line of galvanizing did not allow galvanizing properly continuous, hot, dip, steel containing such oxidizable elements according to such proportions because, as already explained, during the heating and holding treatment at high temperature, a very thin layer of oxide of these addition elements formed on the surface and kept it in the molten zinc which caused defects in the coating.
  • the strip 1 in zone 8 to an oxidation treatment under atmospheric, temperature and residence times such as addition items oxidizable including Si, Cr, Mn or Mo, are oxidized under the surface of the tape before they could migrate to this surface to form a layer oxide capable of causing defects in galvanizing.
  • iron oxides are formed on the surface of the strip. These iron oxides are reduced in the oven enclosure 3 so that the strip 1, when it enters the molten zinc bath 2 has a surface with an oxide layer of reduced addition elements which allows good galvanizing.
  • Zone 8 includes a heating means for carrying the strip 1 at the desired temperature, typically between 150 ° C and 400 ° C.
  • a means of control 7 consisting of a calculator or a computer is provided to adjust the heating of the strip from sensors such as 4 band speed sensors, of temperature 5 and emissivity 6 of the surface of the bandaged.
  • the control of the oxidation kinetics results, in function of a given oxidizing atmosphere, the control of the final temperature of strip 1 in output of the heating means 8 and the residence time of strip 1 in zone 8 and between zone 8 and the inlet of the oven 3.
  • the combination of these parameters is optimized according to the grade of steel to process, line speed and thickness and of the width of the strip.
  • the heating means 8 is chosen to have a low thermal inertia and high reactivity so maintain control of surface oxidation of the band during the transient phases caused by line speed variations or tape format variations 1.
  • This heating medium 8 could be constituted by a gas oven, fire type naked or indirect heating, preferably this means of heating will consist of an induction furnace electromagnetic.
  • the induction oven has at minus an inductor which can be close together or away from the galvanizing furnace to modulate the heating kinetics produced.
  • Band 1 oxidation treatment in zone 8 and between zone 8 and the inlet of oven 3 will be preferably performed in air.
  • Oxidation control of the tape will be achieved then by controlling two parameters: the temperature of the strip at the outlet of 8 and the residence time of the air strip between its entry into zone 8 and entry into oven 3. The temperature should be increased when the speed of the line will increase to compensate for the decrease in high temperature strip residence time in the air.
  • Fig. 2 shows the temperature variation of a point of band 1 plotted on the ordinate as a function of the position of this point on the line carried in abscissa.
  • the strip temperature is low, for example lower than 100 ° C and corresponds to segment 9.
  • the temperature of strip 1 since its exit of the heating means 8 until it enters the oven 3 remains substantially constant as shown by segment 11, the oxidation treatment is continues during this phase. In the oven 3 enclosure, the heating of strip 1 will continue according to a cycle adapted to its metallurgy and symbolized by 12.
  • Tape oxidation control can be performed by action on one or more of parameters presented in Fig. 2. It is possible act on the temperature of the strip by varying the average slope of segment 10 to obtain a level variable of the level of segment 11. It is possible also to vary the duration of step 11 or modify the efficiency of the band oxidation during the level 11, for example by varying the oxygen concentration of the oxidizing atmosphere at which is exposed the tape during this level of treatment.
  • Fig. 3 shows a variant of FIG. 1 in which the heating zone 8 is so connected watertight at the inlet of the oven 3 through the enclosure 13.
  • the heating zone 8 is so connected watertight at the inlet of the oven 3 through the enclosure 13.
  • enclosure 13 it is possible to control the oxygen concentration so that adapt the oxidation of the strip to the specific type steel, belt speed or whatever parameter necessary for controlling the kinematics band oxidation.
  • Oxygen rate control of enclosure 13 as well as the seals of this enclosure vis-à-vis the outside or the enclosure of the oven 3 will be made according to the means of the state of art.
  • Control of the duration of the oxidation treatment in function of line operating parameters can be advantageously carried out by the modification of the length of strip 1 between the outlet of the means of heating 8 and the oven inlet 3. This variation of length can be carried out in various ways.
  • a first possibility consists in moving the means heating 8 in the direction of the strip 1 as illustrated schematically in FIG. 4 by the arrow in dashes 14. For a given tape speed, when the heating means 8 is brought closer to the oven 3, the duration of processing decreases while when the means of heater 8 is away from oven 3, the duration of treatment increases.
  • FIG. 5 A second possibility is illustrated in FIG. 5.
  • the heating means 8 are fixed. Between the means heating 8 and the oven 3, the strip 1 passes over a fixed roller 15 and on a mobile roller 16 which can be moved parallel to the direction of the tape as shown schematically by arrow 17.
  • the moving roller 16 When the moving roller 16 is moved towards the right the strip length between the means of heating 8 and the oven 3 increases which increases the duration of the oxidation treatment. Conversely, when the moving roller 16 is moved to the left of the Fig. 5, the strip length decreases which reduces the duration of treatment.
  • This arrangement with a roller mobile 16 and two horizontal strands of tape can be repeated several times with multiple rollers and several strands of variable length in order to increase the strip length between 8 and 3 and increase the possibility of variation of this length.
  • Fig. 6 shows a variant of FIG. 5 for which the heating means 8 are fixed and the strip 1 passes over two fixed rollers 20 and 21 and over a movable roller 19 which can be moved perpendicular to the main direction of the strip as shown schematically by arrow 18.
  • the moving roller 19 is moved upwards, the strip length between the heating means 8 and the oven 3 increases which increases the duration of the oxidation treatment.
  • the roller mobile 19 is moved down in FIG. 6, the strip length decreases which reduces the duration of the treatment.
  • This arrangement with a roller 19 and two vertical strands of tape can be repeated several times to increase the tape length between 8 and 3 and increase the possibility of variation of this length.
  • rollers 15 and 17 of FIG. 5 or the rollers 19, 20 and 21 of FIG. 6 in an enclosure such as 13 in which the oxygen concentration can be controlled and adjusted to the treatment to be obtained.
  • the band 1 arrives in the molten zinc bath 2 with a surface on which the formation of oxides has been limited, including for elemental oxides of addition, so that the adhesion of zinc on this surface can be done at best.
  • the galvanizing line according to the invention constitutes a flexible production tool allowing economically galvanize various steel grades whatever the nature of their flawless additives of deposition of zinc on their surface.
  • the necessary devices the implementation of the control process the oxidation of the bands comprising additives such as If, Cr, Mn, Mo ... can be easily added to a existing facility to expand its range of production or, on a facility where they are installed, they can be easily disabled to the production of steel grades not including these additives.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Thermal Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Combustion & Propulsion (AREA)
  • General Engineering & Computer Science (AREA)
  • Coating With Molten Metal (AREA)
  • Heat Treatment Of Strip Materials And Filament Materials (AREA)
  • Electroplating Methods And Accessories (AREA)

Abstract

Procédé de galvanisation en continu à chaud au trempé d'une bande d'acier (1) comportant des éléments d'addition oxydables en une proportion permettant d'améliorer les propriétés mécaniques de l'acier, selon lequel la bande chemine dans un four de galvanisation (3) sous une atmosphère réductrice, ce four étant constitué de sections de traitement thermique, de chauffage, de maintien, de refroidissement et de trempé dans un bain de galvanisation (2). La bande est soumise, en amont de la section d'entrée du four, à un traitement d'oxydation dans des conditions de température, de durée et de teneur en oxygène d'un gaz dans lequel baigne la bande, telles que les éléments d'addition oxydables soient oxydés essentiellement à l'intérieur de la bande, avant qu'ils n'aient pu migrer vers la surface pour y former une couche d'oxyde. <IMAGE>Process for continuous hot dip galvanizing of a steel strip (1) comprising oxidizable addition elements in a proportion making it possible to improve the mechanical properties of steel, according to which the strip travels in a galvanizing (3) under a reducing atmosphere, this furnace consisting of sections for heat treatment, heating, holding, cooling and quenching in a galvanizing bath (2). The strip is subjected, upstream of the inlet section of the furnace, to an oxidation treatment under conditions of temperature, duration and oxygen content of a gas in which the strip is bathed, such as the elements of The oxidizable additions are essentially oxidized inside the strip, before they can migrate to the surface to form an oxide layer there. <IMAGE>

Description

L'invention est relative à un procédé de galvanisation en continu à chaud au trempé d'une bande d'acier comportant des éléments d'addition oxydables en une proportion permettant d'améliorer les propriétés mécaniques de l'acier.The invention relates to a galvanizing process continuously hot by dipping a steel strip having oxidizable additives in one proportion to improve properties steel mechanics.

L'amélioration des propriétés mécaniques de l'acier va aussi bien vers l'augmentation des résistances mécaniques visant par exemple à diminuer leur épaisseur et donc le poids d'acier, que vers l'augmentation de l'emboutissabilité, ou encore vers l'augmentation de ces deux critères. Ceci à conduit à la mise au point de nuances d'aciers multiphasés, par exemple de type DP (dual phase) et TRIP (Transformation induite par plasticité) .The improvement of the mechanical properties of steel will as well towards increasing resistances mechanical for example aimed at reducing their thickness and therefore the weight of steel, that towards the increase of stampability, or even towards increasing these two criteria. This led to the development of grades of multiphase steels, for example of the DP type (dual phase) and TRIP (Transformation induced by plasticity).

Ces nuances multiphasées à très haute résistance sont généralement obtenues par addition d'éléments durcisseurs tels que Si, Mn, Cr, Mo, etc. Les fours de galvanisation à chaud au trempé selon l'état de la technique comportent typiquement plusieurs sections équipées pour réaliser des différentes phases du traitement thermique qui sont généralement : chauffage, maintien, refroidissement. Le four de traitement thermique est conditionné par une atmosphère neutre ou réductrice, généralement constituée d'un mélange d'azote et d'hydrogène destiné à réduire les oxydes de fer présents à la surface des tôles avant leur galvanisation.These very high resistance multiphase grades are generally obtained by adding elements hardeners such as Si, Mn, Cr, Mo, etc. Hot dip galvanizing ovens according to the state of the art typically comprise several sections equipped to carry out different phases heat treatment which are generally: heating, holding, cooling. The oven heat treatment is conditioned by an atmosphere neutral or reducing, generally consisting of mixture of nitrogen and hydrogen to reduce iron oxides present on the surface of the front plates their galvanization.

On constate que, pour les aciers multiphasés, des éléments présents tels que Si, Mn, Cr, Mo, etc, plus oxydables que le fer se combinent prioritairement avec les atomes d'oxygène présents dans le four pour former des oxydes en surface de la bande. Le potentiel d'oxydation très élevé de ces composants entraíne même une migration de leurs atomes vers la surface de la bande pour qu'ils puissent s'oxyder avec l'oxygène présent dans le four.It can be seen that, for multi-phase steels, elements present such as Si, Mn, Cr, Mo, etc., more oxidizable as iron combine primarily with the oxygen atoms present in the furnace to form oxides at the surface of the strip. The potential very high oxidation of these components even causes a migration of their atoms to the surface of the tape so they can oxidize with oxygen present in the oven.

Le résultat est la formation d'une mince couche d'oxydes à la surface de la bande. Ces oxydes sont stables et ne sont pas réduits lors de leur passage dans les différentes zones du four, on les retrouve donc à la surface de la bande lors de sa plongée dans le bain de zinc ce qui fait obstacle à l'adhérence du zinc durant l'opération de galvanisation. La diminution du point de rosée de l'atmosphère du four dans les limites compatibles avec l'état de l'art actuel n'a pas supprimé ce phénomène et on constate toujours la présence sur la surface des bandes galvanisées de défauts provoqués par la présence locale de ces oxydes.The result is the formation of a thin layer oxides on the surface of the strip. These oxides are stable and are not reduced during their passage in the different areas of the oven, we find them so on the surface of the strip when diving into the zinc bath which obstructs the adhesion of the zinc during the galvanizing operation. Reduction the dew point of the furnace atmosphere in the limits compatible with the current state of the art has not removed this phenomenon and we still see the presence on the surface of the galvanized strips of faults caused by the local presence of these oxides.

Il en résulte que actuellement le procédé de galvanisation au trempé d'une bande d'acier ne permet pas de galvaniser correctement les nuances d'acier multiphasés ayant une teneur en éléments oxydables tels que Si, Cr, Mn, Mo, ... suffisante pour améliorer les propriétés mécaniques de l'acier.It follows that currently the process of dip galvanizing of a steel strip does not allow not to properly galvanize steel grades multiphase having a content of oxidizable elements such that Si, Cr, Mn, Mo, ... sufficient to improve the mechanical properties of steel.

L'invention proposée a pour but de fournir un dispositif et un procédé de galvanisation à chaud au trempé en continu qui permettent de traiter correctement des bandes contenant des éléments d'addition oxydables dont la teneur est suffisante pour améliorer les propriétés mécaniques de l'acier.The object of the proposed invention is to provide a device and method for hot-dip galvanizing continuously tempered which allow to process correctly bands containing elements of oxidizable addition the content of which is sufficient for improve the mechanical properties of steel.

L'invention concerne une ligne de galvanisation en continu à chaud au trempé d'une bande d'acier comportant des éléments d'addition oxydables en une proportion permettant d'améliorer les propriétés mécaniques de l'acier, selon laquelle la bande chemine dans un four de galvanisation sous une atmosphère réductrice, avec trempé dans un bain de galvanisation, cette ligne étant caractérisée en ce qu'elle comprend en amont du four de galvanisation un moyen de chauffage de la bande à une température appropriée suivi d'une zone pour exposer la bande à une atmosphère oxydante dont la teneur en oxygène est telle que, compte tenu de la température de la bande et de la durée du traitement, les éléments d'addition oxydables de la bande d'acier soient oxydés à la surface et immédiatement sous la surface de la bande avant qu'ils n'aient pu migrer vers ladite surface pour y former une couche d'oxydes capable de provoquer des défauts de galvanisation. Les oxydes de fer produits durant cette opération seront réduits durant le passage de la bande dans le four.The invention relates to a galvanizing line in continuous hot with the dip of a steel strip having oxidizable additives in one proportion to improve properties steel mechanics, according to which the strip travels in a galvanizing furnace under an atmosphere reducing, with soaking in a galvanizing bath, this line being characterized in that it comprises upstream of the galvanizing furnace a heating means tape at an appropriate temperature followed by area to expose the strip to an oxidizing atmosphere whose oxygen content is such that, taking into account the strip temperature and the duration of the treatment, the oxidizable addition elements of the steel strip be oxidized on the surface and immediately below the surface of the strip before they could not migrate to said surface to form a layer of oxides capable of causing defects in galvanizing. The iron oxides produced during this operation will be reduced during the passage of the tape in the oven.

Avantageusement, la bande est portée à une température comprise entre 150 °C et 400 °C, de préférence entre 150°C et 300°C environ, pour le traitement d'oxydation. Pour une nuance d'acier donnée, le contrôle de l'oxydation de sa surface, pour une atmosphère oxydante donnée, sera effectué par le choix du couple température / temps de séjour de la bande dans l'atmosphère oxydante. Advantageously, the strip is brought to a temperature between 150 ° C and 400 ° C, preferably between 150 ° C and 300 ° C approximately, for the oxidation treatment. For a given steel grade, the control of the oxidation of its surface, for an oxidizing atmosphere given, will be made by the choice of the couple strip temperature / residence time in the oxidizing atmosphere.

Le contrôle de ce couple température / temps de séjour sera effectué en continu et tiendra compte du régime de fonctionnement de la ligne, en particulier de la vitesse instantanée de défilement de la bande. Le contrôle du traitement d'oxydation de la bande peut être effectué en régulant la puissance de chauffage situé en amont du four (action sur la température de la bande) ou en agissant sur la distance entre l'élément chauffant situé en amont du four et l'entrée du four (action sur le temps d'oxydation).Control of this temperature / residence time couple will be carried out continuously and will take into account the operation of the line, in particular the instant tape speed. The control of the tape oxidation treatment can be carried out by regulating the heating power located upstream of the oven (action on the temperature of the band) or by acting on the distance between the element heater located upstream of the oven and the oven inlet (action on the oxidation time).

L'atmosphère oxydante dans laquelle s'effectue l'opération contrôlée d'oxydation de la surface de la bande peut être l'air ambiant ou tout autre atmosphère confinée dans une enceinte installée en amont du four et dont on contrôlera la teneur en oxygène.The oxidizing atmosphere in which takes place the controlled oxidation operation of the surface of the tape can be ambient air or any other atmosphere confined in an enclosure installed upstream of the oven and whose oxygen content will be checked.

L'invention consiste, mises à part les dispositions exposées ci-dessus, en un certain nombre d'autres dispositions dont il sera plus explicitement question ci-après à propos d'exemples de réalisations décrits en détail avec références aux dessins annexés, mais qui ne sont nullement limitatifs.

  • Fig. 1 est un schéma d'une ligne de galvanisation en continu à chaud au trempé mettant en oeuvre le procédé de l'invention,
  • Fig. 2 est un diagramme représentant la variation de la température d'un point de la bande, portée en ordonnée, en fonction de la position du point sur la ligne présenté en abscisse,
  • Fig. 3 est un schéma d'une variante de la ligne de galvanisation,
  • Fig. 4 à 6 sont des autres variantes de réalisation.
The invention consists, apart from the arrangements set out above, of a certain number of other arrangements which will be more explicitly discussed below in connection with examples of embodiments described in detail with reference to the appended drawings, but which are in no way limiting.
  • Fig. 1 is a diagram of a continuous hot dip galvanizing line implementing the method of the invention,
  • Fig. 2 is a diagram representing the variation of the temperature of a point of the strip, plotted on the ordinate, as a function of the position of the point on the line presented on the abscissa,
  • Fig. 3 is a diagram of a variant of the galvanizing line,
  • Fig. 4 to 6 are other alternative embodiments.

Pour les Fig. 1 à 4, la bande se déplace de la gauche vers la droite.For Figs. 1 to 4, the strip moves from the left to the right.

En se reportant à la Fig. 1 des dessins, on peut voir, schématiquement représentée, une ligne de galvanisation en continu à chaud au trempé d'une bande d'acier 1 dans un bain de galvanisation de zinc en fusion 2.Referring to FIG. 1 of the drawings, we can see, schematically shown, a galvanizing line continuously hot by dipping a steel strip 1 in a zinc galvanizing bath in fusion 2.

La ligne comprend un four de galvanisation réalisé suivant l'état de l'art 3 pour le traitement de la bande 1 avant son trempé dans le bain 2. Le four comprend plusieurs sections équipées pour réaliser successivement les différentes phases du traitement thermique qui sont généralement chauffage, maintien puis refroidissement jusqu'à une température adaptée à la déposition du zinc à la surface de la bande. L'atmosphère du four 3 est réductrice, réalisée par un mélange de gaz traditionnellement d'azote avec de l'hydrogène avec un point de rosée maintenu aussi bas que possible.The line includes a galvanizing oven produced according to state of the art 3 for the treatment of strip 1 before its soaking in the bath 2. The oven includes several sections equipped to carry out successively the different phases of the treatment which are generally heating, maintaining then cooling to a temperature suitable for the deposition of zinc on the surface of the strip. The atmosphere of the oven 3 is reducing, produced by a mixture of gases traditionally nitrogen with hydrogen with a dew point kept as low as possible.

La bande l'acier 1 contient des éléments d'addition oxydables tels que Si, Cr, Mn, Mo selon des proportions suffisantes pour améliorer ses caractéristiques mécaniques. Jusqu'à ce jour, ce type de ligne de galvanisation ne permettait pas de galvaniser correctement en continu , à chaud, au trempé, un acier contenant de tels éléments oxydables suivant de telles proportions car, comme déjà expliqué, lors du traitement de chauffage et de maintien à haute température, une très mince couche d'oxyde de ces éléments d'addition se formait en surface et se maintenait jusque dans le zinc fondu ce qui provoquait des défauts dans le revêtement. The steel strip 1 contains addition elements oxidizable such as Si, Cr, Mn, Mo in proportions sufficient to improve its characteristics mechanical. To date, this type of line of galvanizing did not allow galvanizing properly continuous, hot, dip, steel containing such oxidizable elements according to such proportions because, as already explained, during the heating and holding treatment at high temperature, a very thin layer of oxide of these addition elements formed on the surface and kept it in the molten zinc which caused defects in the coating.

Selon l'invention, en amont du four 3 on soumet la bande 1 dans une zone 8 à un traitement d'oxydation dans des conditions d'atmosphère, de température et de temps de séjour telles que les éléments d'addition oxydables notamment Si, Cr, Mn ou Mo, soient oxydés sous la surface de la bande avant qu'ils n'aient pu migrer vers cette surface pour former une couche d'oxyde à même de provoquer des défauts de galvanisation.According to the invention, upstream of the furnace 3, the strip 1 in zone 8 to an oxidation treatment under atmospheric, temperature and residence times such as addition items oxidizable including Si, Cr, Mn or Mo, are oxidized under the surface of the tape before they could migrate to this surface to form a layer oxide capable of causing defects in galvanizing.

Dans ces conditions, lors du traitement dans la chambre 3, les oxydes d'éléments d'addition restent piégés à l'intérieur du matériau et il n'y a plus de migration d'éléments d'addition vers la surface de la bande à même d'enrichir la couche d'oxydes jusqu'à provoquer des défauts de galvanisation.Under these conditions, during treatment in the room 3, the oxides of addition elements remain trapped at inside the material and there is no more migration of additives to the surface of the strip to even enrich the oxide layer to the point of causing galvanizing faults.

Lors du traitement dans la zone 8 et de la zone 8 jusqu'à l'entrée du four, des oxydes de fer sont formés à la surface de la bande. Ces oxydes de fer sont réduits dans l'enceinte du four 3 de sorte que la bande 1, lorsqu'elle arrive dans le bain de zinc fondu 2 présente une surface présentant une couche d'oxydes d'éléments d'addition réduite qui permet une bonne galvanisation.When processing in zone 8 and zone 8 up to the oven entrance, iron oxides are formed on the surface of the strip. These iron oxides are reduced in the oven enclosure 3 so that the strip 1, when it enters the molten zinc bath 2 has a surface with an oxide layer of reduced addition elements which allows good galvanizing.

La zone 8 comporte un moyen de chauffage pour porter la bande 1 à la température souhaitée, typiquement comprise entre 150 °C et 400 °C. Un moyen de contrôle 7 constitué par un calculateur ou un ordinateur est prévu pour ajuster le chauffage de la bande à partir de capteurs tels que des capteurs de vitesse de bande 4, de température 5 et d'émissivité 6 de la surface de la bande.Zone 8 includes a heating means for carrying the strip 1 at the desired temperature, typically between 150 ° C and 400 ° C. A means of control 7 consisting of a calculator or a computer is provided to adjust the heating of the strip from sensors such as 4 band speed sensors, of temperature 5 and emissivity 6 of the surface of the bandaged.

Le contrôle de la cinétique d'oxydation résulte, en fonction d'une atmosphère oxydante donnée, de la maítrise de la température finale de la bande 1 en sortie du moyen de chauffage 8 et du temps de séjour de la bande 1 dans la zone 8 et entre la zone 8 et l'entrée du four 3. La combinaison de ces paramètres est optimisée en fonction de la nuance de l'acier à traiter, de la vitesse de la ligne et de l'épaisseur et de la largeur de la bande.The control of the oxidation kinetics results, in function of a given oxidizing atmosphere, the control of the final temperature of strip 1 in output of the heating means 8 and the residence time of strip 1 in zone 8 and between zone 8 and the inlet of the oven 3. The combination of these parameters is optimized according to the grade of steel to process, line speed and thickness and of the width of the strip.

Le moyen de chauffage 8 est choisi pour avoir une faible inertie thermique et une forte réactivité afin de maintenir un contrôle de l'oxydation de la surface de la bande durant les phases transitoires occasionnées par les variations de vitesse de la ligne ou les variations de format de bande 1. Ce moyen de chauffage 8 pourra être constitué par un four à gaz, de type feu nu ou chauffage indirect, de préférence ce moyen de chauffage sera constitué par un four à induction électromagnétique. Le four à induction comporte au moins une bobine inductrice qui peut être rapprochée ou éloignée du four de galvanisation pour moduler la cinétique d'échauffement produite.The heating means 8 is chosen to have a low thermal inertia and high reactivity so maintain control of surface oxidation of the band during the transient phases caused by line speed variations or tape format variations 1. This heating medium 8 could be constituted by a gas oven, fire type naked or indirect heating, preferably this means of heating will consist of an induction furnace electromagnetic. The induction oven has at minus an inductor which can be close together or away from the galvanizing furnace to modulate the heating kinetics produced.

Le traitement d'oxydation de la bande 1 dans la zone 8 et entre la zone 8 et l'entrée du four 3 sera de préférence effectué à l'air. Le contrôle de l'oxydation de la bande sera réalisé alors par le contrôle de deux paramètres : la température de la bande en sortie de 8 et le temps de séjour de la bande à l'air entre son entrée dans la zone 8 et son entrée dans le four 3. La température devra être augmentée quand la vitesse de la ligne augmentera afin de compenser la diminution du temps de séjour de la bande à haute température dans l'air. Band 1 oxidation treatment in zone 8 and between zone 8 and the inlet of oven 3 will be preferably performed in air. Oxidation control of the tape will be achieved then by controlling two parameters: the temperature of the strip at the outlet of 8 and the residence time of the air strip between its entry into zone 8 and entry into oven 3. The temperature should be increased when the speed of the line will increase to compensate for the decrease in high temperature strip residence time in the air.

La Fig. 2 présente la variation de température d'un point de la bande 1 portée en ordonnée en fonction de la position de ce point sur la ligne portée en abscisse. En amont du moyen de chauffage 8, la température de la bande est basse, par exemple inférieure à 100 °C et correspond au segment 9. Lors du passage de la bande 1 dans le moyen de chauffage 8, sa température augmente suivant, par exemple, le segment incliné 10. La température de la bande 1, depuis sa sortie du moyen de chauffage 8 jusqu'à son entrée dans le four 3 reste sensiblement constante comme schématisé par le segment 11, le traitement d'oxydation se poursuit durant cette phase. Dans l'enceinte du four 3, le chauffage de la bande 1 va continuer suivant un cycle adapté à sa métallurgie et symbolisé par 12.Fig. 2 shows the temperature variation of a point of band 1 plotted on the ordinate as a function of the position of this point on the line carried in abscissa. Upstream of the heating means 8, the strip temperature is low, for example lower than 100 ° C and corresponds to segment 9. When passage of the strip 1 in the heating means 8, its temperature increases depending, for example, on the segment inclined 10. The temperature of strip 1, since its exit of the heating means 8 until it enters the oven 3 remains substantially constant as shown by segment 11, the oxidation treatment is continues during this phase. In the oven 3 enclosure, the heating of strip 1 will continue according to a cycle adapted to its metallurgy and symbolized by 12.

Le contrôle de l'oxydation de la bande peut être effectué par action sur l'un ou plusieurs des paramètres présentés sur la Fig. 2. Il est possible d'agir sur la température de la bande en faisant varier la pente moyenne du segment 10 pour obtenir un niveau variable du palier du segment 11. Il est possible également de faire varier la durée du palier 11 ou de modifier l'efficacité de l'oxydation de la bande durant le palier 11, par exemple en faisant varier la concentration d'oxygène de l'atmosphère oxydante à laquelle est exposée la bande durant ce palier de traitement.Tape oxidation control can be performed by action on one or more of parameters presented in Fig. 2. It is possible act on the temperature of the strip by varying the average slope of segment 10 to obtain a level variable of the level of segment 11. It is possible also to vary the duration of step 11 or modify the efficiency of the band oxidation during the level 11, for example by varying the oxygen concentration of the oxidizing atmosphere at which is exposed the tape during this level of treatment.

La Fig. 3 présente une variante de la Fig. 1 dans laquelle la zone de chauffage 8 est reliée de façon étanche à l'entrée du four 3 par l'enceinte 13. On comprend que, au sein de l'enceinte 13, il est possible de contrôler la concentration en oxygène de façon à adapter l'oxydation de la bande au type spécifique d'acier, à la vitesse de bande ou à tout autre paramètre nécessaire au contrôle de la cinématique d'oxydation de la bande. Le contrôle du taux d'oxygène de l'enceinte 13 ainsi que les étanchéités de cette enceinte vis à vis de l'extérieur ou de l'enceinte du four 3 seront réalisés suivant les moyens de l'état de l'art.Fig. 3 shows a variant of FIG. 1 in which the heating zone 8 is so connected watertight at the inlet of the oven 3 through the enclosure 13. On understands that, within enclosure 13, it is possible to control the oxygen concentration so that adapt the oxidation of the strip to the specific type steel, belt speed or whatever parameter necessary for controlling the kinematics band oxidation. Oxygen rate control of enclosure 13 as well as the seals of this enclosure vis-à-vis the outside or the enclosure of the oven 3 will be made according to the means of the state of art.

Le contrôle de la durée du traitement d'oxydation en fonction des paramètres de fonctionnement de la ligne peut être avantageusement effectué par la modification de la longueur de bande 1 entre la sortie du moyen de chauffage 8 et l'entrée du four 3. Cette variation de longueur peut être effectuée de diverses manières.Control of the duration of the oxidation treatment in function of line operating parameters can be advantageously carried out by the modification of the length of strip 1 between the outlet of the means of heating 8 and the oven inlet 3. This variation of length can be carried out in various ways.

Une première possibilité consiste à déplacer le moyen de chauffage 8 suivant la direction de la bande 1 comme illustré schématiquement sur la Fig. 4 par la flèche en tirets 14. Pour une vitesse de bande donnée, lorsque le moyen de chauffage 8 est rapproché du four 3, la durée de traitement diminue tandis que lorsque le moyen de chauffage 8 est éloigné du four 3, la durée du traitement augmente.A first possibility consists in moving the means heating 8 in the direction of the strip 1 as illustrated schematically in FIG. 4 by the arrow in dashes 14. For a given tape speed, when the heating means 8 is brought closer to the oven 3, the duration of processing decreases while when the means of heater 8 is away from oven 3, the duration of treatment increases.

Une deuxième possibilité est illustrée par la Fig. 5. Les moyens de chauffage 8 sont fixes. Entre les moyens de chauffage 8 et le four 3, la bande 1 passe sur un rouleau fixe 15 et sur un rouleau mobile 16 pouvant être déplacé parallèlement à la direction de la bande comme illustré schématiquement par la flèche 17. Lorsque le rouleau mobile 16 est déplacé vers la droite, la longueur de bande entre les moyens de chauffage 8 et le four 3 augmente ce qui augmente la durée du traitement d'oxydation. Inversement, lorsque le rouleau mobile 16 est déplacé vers la gauche de la Fig. 5, la longueur de bande diminue ce qui réduit la durée du traitement. Cette disposition avec un rouleau mobile 16 et deux brins horizontaux de bande peut être répétée plusieurs fois avec plusieurs rouleaux et plusieurs brins de longueur variable afin d'augmenter la longueur de bande entre 8 et 3 et augmenter la possibilité de variation de cette longueur.A second possibility is illustrated in FIG. 5. The heating means 8 are fixed. Between the means heating 8 and the oven 3, the strip 1 passes over a fixed roller 15 and on a mobile roller 16 which can be moved parallel to the direction of the tape as shown schematically by arrow 17. When the moving roller 16 is moved towards the right the strip length between the means of heating 8 and the oven 3 increases which increases the duration of the oxidation treatment. Conversely, when the moving roller 16 is moved to the left of the Fig. 5, the strip length decreases which reduces the duration of treatment. This arrangement with a roller mobile 16 and two horizontal strands of tape can be repeated several times with multiple rollers and several strands of variable length in order to increase the strip length between 8 and 3 and increase the possibility of variation of this length.

La Fig. 6 présente une variante de la Fig. 5 pour laquelle les moyens de chauffage 8 sont fixes et la bande 1 passe sur deux rouleaux fixes 20 et 21 et sur un rouleau mobile 19 pouvant être déplacé perpendiculairement à la direction principale de la bande comme illustré schématiquement par la flèche 18. Lorsque le rouleau mobile 19 est déplacé vers le haut, la longueur de bande entre les moyens de chauffage 8 et le four 3 augmente ce qui augmente la durée du traitement d'oxydation. Inversement, lorsque le rouleau mobile 19 est déplacé vers le bas de la Fig. 6, la longueur de bande diminue ce qui réduit la durée du traitement. Cette disposition avec un rouleau 19 et deux brins verticaux de bande peut être répétée plusieurs fois afin d'augmenter la longueur de bande entre 8 et 3 et augmenter la possibilité de variation de cette longueur.Fig. 6 shows a variant of FIG. 5 for which the heating means 8 are fixed and the strip 1 passes over two fixed rollers 20 and 21 and over a movable roller 19 which can be moved perpendicular to the main direction of the strip as shown schematically by arrow 18. When the moving roller 19 is moved upwards, the strip length between the heating means 8 and the oven 3 increases which increases the duration of the oxidation treatment. Conversely, when the roller mobile 19 is moved down in FIG. 6, the strip length decreases which reduces the duration of the treatment. This arrangement with a roller 19 and two vertical strands of tape can be repeated several times to increase the tape length between 8 and 3 and increase the possibility of variation of this length.

On comprend que toutes les combinaisons de rouleaux fixes et de rouleaux mobiles permettant de faire varier la longueur de bande entre les moyens de chauffage 8 et l'entrée du four 3 permettent de faire varier la durée de l'oxydation de la bande et peuvent être mises en oeuvre dans le cadre de cette invention.We understand that all combinations of rollers fixed and movable rollers to vary the strip length between the heating means 8 and the inlet of the oven 3 allows the duration to be varied band oxidation and can be brought in work in the context of this invention.

Il est également possible de placer les rouleaux 15 et 17 de la Fig. 5 ou les rouleaux 19, 20 et 21 de la Fig. 6 dans une enceinte telle que 13 dans laquelle la concentration en oxygène peut être contrôlée et ajustée au traitement à obtenir.It is also possible to place the rollers 15 and 17 of FIG. 5 or the rollers 19, 20 and 21 of FIG. 6 in an enclosure such as 13 in which the oxygen concentration can be controlled and adjusted to the treatment to be obtained.

On comprend également qu'il est possible de combiner le contrôle de la température de sortie de la bande des moyens de chauffage 8 et le contrôle de la durée de l'oxydation en fonction des caractéristiques du matériau et des objectifs visés. Ce contrôle de la température et du temps de traitement ainsi que la commande des actionneurs correspondants est réalisé par le calculateur 7 en fonction des données du produits saisies par l'opérateur ainsi que par les mesures réalisées par les capteurs tels que, par exemple, 4, 5 et 6.We also understand that it is possible to combine the tape outlet temperature control heating means 8 and control of the duration of oxidation depending on the characteristics of the material and objectives. This control of the temperature and processing time as well as the control of the corresponding actuators is carried out by calculator 7 based on product data entered by the operator as well as by the measurements performed by sensors such as, for example, 4, 5 and 6.

Grâce à la mise en oeuvre de ces dispositifs, la bande 1 arrive dans le bain de zinc en fusion 2 avec une surface sur laquelle la formation des oxydes a été limitée, y compris pour les oxydes des éléments d'addition, de sorte que l'adhérence du zinc sur cette surface puisse s'effectuer au mieux.Thanks to the implementation of these devices, the band 1 arrives in the molten zinc bath 2 with a surface on which the formation of oxides has been limited, including for elemental oxides of addition, so that the adhesion of zinc on this surface can be done at best.

La ligne de galvanisation selon l'invention constitue un outil de production flexible permettant de galvaniser économiquement diverses nuances d'acier quelle que soit la nature de leurs additifs sans défaut de déposition du zinc sur leur surface. Les moyens de contrôle 7 et les moyens de chauffage 8, grâce à leur rapidité d'adaptation, permettent d'adapter le procédé de contrôle d'oxydation à toutes les dimensions de produits et à toutes les variations de vitesse de la ligne de production.The galvanizing line according to the invention constitutes a flexible production tool allowing economically galvanize various steel grades whatever the nature of their flawless additives of deposition of zinc on their surface. The means of control 7 and the heating means 8, thanks to their rapid adaptation, allow the process to be adapted oxidation control at all dimensions of products and at all the speed variations of the production line.

On peut également noter que les dispositifs nécessaires à la mise en oeuvre du procédé de contrôle de l'oxydation des bandes comprenant des additifs tels que Si, Cr, Mn, Mo... peuvent être facilement ajoutés à une installation existante pour étendre sa gamme de production ou, sur une installation où ils sont installés, ils peuvent être neutralisés facilement pour la production de nuances d'acier ne comprenant pas ces additifs.It can also be noted that the necessary devices the implementation of the control process the oxidation of the bands comprising additives such as If, Cr, Mn, Mo ... can be easily added to a existing facility to expand its range of production or, on a facility where they are installed, they can be easily disabled to the production of steel grades not including these additives.

Claims (12)

Procédé de galvanisation en continu à chaud au trempé d'une bande d'acier (1) comportant des éléments d'addition oxydables en une proportion permettant d'améliorer les propriétés mécaniques de l'acier, selon lequel la bande chemine dans un four de galvanisation (3) sous une atmosphère réductrice, ce four étant constitué de sections de traitement thermique, de chauffage, de maintien, de refroidissement et de trempé dans un bain de galvanisation (2),la bande ayant été soumise à un traitement d'oxydation dans des conditions de température, de durée et de teneur en oxygène d'un gaz dans lequel baigne la bande, telles que les éléments d'addition oxydables soient oxydés essentiellement à l'intérieur de la bande, avant qu'ils n'aient pu migrer vers la surface pour y former une couche d'oxydes de nature à créer des défauts de galvanisation,
caractérisé en ce que la bande est soumise au traitement d'oxydation en amont de la section d'entrée du four, que le gaz dans lequel baigne la bande pour le traitement d'oxydation est l'air, que cette bande est portée à une température comprise entre 150°C et 400°C environ pour le traitement d'oxydation, et que le contrôle de l'oxydation à la surface et immédiatement sous la surface de la bande est effectué par contrôle du couple température/temps de telle sorte que la température de la bande d'acier (1) est augmentée lorsque la vitesse de ligne augmente et que le temps de traitement diminue, et inversement.Process for continuous hot dip galvanizing of a steel strip (1) comprising oxidizable addition elements in a proportion making it possible to improve the mechanical properties of steel, according to which the strip travels in a galvanizing (3) under a reducing atmosphere, this furnace being made up of heat treatment, heating, holding, cooling and quenching sections in a galvanizing bath (2), the strip having been subjected to an oxidation treatment under conditions of temperature, duration and oxygen content of a gas in which the strip is bathed, such that the oxidizable additives are oxidized essentially inside the strip, before they have been able to migrate towards the surface to form a layer of oxides of such a nature as to create galvanizing defects,
characterized in that the strip is subjected to the oxidation treatment upstream of the inlet section of the furnace, that the gas in which the strip is bathed for the oxidation treatment is air, that this strip is brought to a temperature between 150 ° C and 400 ° C approximately for the oxidation treatment, and that the oxidation control on the surface and immediately below the surface of the strip is carried out by controlling the temperature / time pair so that the temperature of the steel strip (1) is increased as the line speed increases and the treatment time decreases, and vice versa. Procédé selon la revendication 1, caractérisé en ce que la bande d'acier est portée à une température comprise entre 150°C et 300°C environ pour le traitement d'oxydation.Process according to Claim 1, characterized in that the steel strip is brought to a temperature between approximately 150 ° C and 300 ° C for the oxidation treatment. Procédé selon la revendication 1 ou 2, caractérisé en ce que le contrôle de la température est effectué à partir de la puissance d'un moyen de chauffage (8) de la bande en amont du four de galvanisation. Method according to claim 1 or 2, characterized in that the temperature is controlled from the power of a heating means (8) of the strip upstream of the galvanizing furnace. Procédé selon l'une des revendications 1 à 3, caractérisé en ce que le contrôle de la durée du traitement d'oxydation est effectué par modification de la longueur de bande (1) entre la sortie d'un moyen de chauffage (8) situé en amont du four et l'entrée du four de galvanisation (3).Method according to one of claims 1 to 3, characterized in that the control of the duration of the oxidation treatment is carried out by modification of the strip length (1) between the outlet of a heating means (8) located upstream of the oven and the inlet of the galvanizing oven (3). Procédé selon la revendication 4, caractérisé en ce que la modification de la longueur de bande entre la sortie du moyen de chauffage (8) et l'entrée du four de galvanisation (3) est assurée par déplacement du moyen de chauffage (8) suivant la direction de la bande.Method according to claim 4, characterized in that the modification of the strip length between the outlet of the heating means (8) and the inlet of the galvanizing furnace (3) is ensured by displacement of the heating means (8) according to the direction of the band. Procédé selon la revendication 5, caractérisé en ce que la modification de la longueur de bande entre la sortie du moyen de chauffage (8) et l'entrée du four de galvanisation (3) est assurée par réglage de la longueur d'au moins un brin vertical ou horizontal de la bande, ou une combinaison des deux.Method according to claim 5, characterized in that the modification of the strip length between the outlet of the heating means (8) and the inlet of the galvanizing furnace (3) is ensured by adjusting the length of at least one vertical or horizontal strand of the strip, or a combination of both. Ligne de galvanisation en continu à chaud au trempé d'une bande d'acier (1) comportant des éléments d'addition oxydables en une proportion permettant d'améliorer les propriétés mécaniques de l'acier, selon laquelle la bande chemine dans un four de galvanisation (3) sous une atmosphère réductrice, avec trempé dans un bain de galvanisation (2), caractérisée en ce qu'elle comprend en amont du four de galvanisation un moyen de chauffage (8) de la bande à une température comprise entre 150°C et 400°C environ, et une zone pour exposer la bande à un gaz d'oxydation dont la teneur en oxygène est telle que, compte tenu de la température et de la durée de traitement, les éléments d'addition oxydables de la bande d'acier soient oxydés à l'intérieur de cette bande avant qu'ils n'aient pu migrer vers la surface pour y former une couche d'oxyde. Continuous hot dip galvanizing line of a steel strip (1) comprising addition elements oxidizable in a proportion allowing the mechanical properties of the steel to be improved, according to which the strip travels in a galvanizing (3) under a reducing atmosphere, with quenching in a galvanizing bath (2), characterized in that it comprises, upstream of the galvanizing furnace, a means of heating (8) of the strip at a temperature between 150 ° C and approximately 400 ° C., and an area for exposing the strip to an oxidation gas whose oxygen content is such that, taking into account the temperature and the duration of treatment, the oxidizable addition elements of the strip steel are oxidized inside this strip before they can migrate to the surface to form an oxide layer. Ligne de galvanisation selon la revendication 9, caractérisée en ce que le moyen de chauffage (8) est constitué par un four à induction qui constitue également la zone pour exposer la bande à un gaz d'oxydation.Galvanizing line according to claim 9, characterized in that the heating means (8) consists of an induction furnace which also constitutes the zone for exposing the strip to an oxidation gas. Ligne de galvanisation selon la revendication 7 ou 8, caractérisée en ce que la zone de chauffage (8) est reliée de façon étanche à l'entrée du four (3) par une enceinte (13) dans laquelle la concentration en oxygène peut être contrôlée et ajustée au traitement à obtenir.Galvanizing line according to claim 7 or 8, characterized in that the heating zone (8) is tightly connected to the inlet of the oven (3) by an enclosure (13) in which the oxygen concentration can be controlled and adjusted to the treatment to be obtained. Ligne de galvanisation selon la revendication 8, caractérisée en ce que le four à induction comporte au moins une bobine inductrice qui peut être rapprochée ou éloignée du four de galvanisation pour moduler la cinétique d'échauffement produite.Galvanizing line according to claim 8, characterized in that the induction furnace comprises at least one induction coil which can be brought close to or distant from the galvanizing furnace to modulate the heating kinetics produced. Ligne de galvanisation selon la revendication 7, caractérisée en ce que le moyen de chauffage est constitué par un four à gaz.Galvanizing line according to claim 7, characterized in that the heating means is constituted by a gas oven. Ligne de galvanisation selon l'une des revendications 7 à 11, caractérisée en ce que qu'elle comprend un moyen de contrôle (7) propre à agir sur le moyen de chauffage (8) pour maintenir la bande à une température déterminée à la sortie du moyen de chauffage, en réponse à des informations fournies par des capteurs (4,5,6).Galvanizing line according to one of claims 7 to 11, characterized in that it comprises a control means (7) capable of acting on the heating means (8) to maintain the strip at a determined temperature at the outlet heating means, in response to information provided by sensors (4,5,6).
EP04290508A 2003-03-12 2004-02-25 Method for the control of oxidation of sheets before hot dip galvanizing and galvanizing line Withdrawn EP1457580A1 (en)

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FR0303058 2003-03-12
FR0303058A FR2852330B1 (en) 2003-03-12 2003-03-12 METHOD OF CONTROLLED OXIDATION OF STRIPS BEFORE CONTINUOUS GALVANIZATION AND LINE OF GALVANIZATION

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DE (1) DE04290508T1 (en)
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CN1530458A (en) 2004-09-22
KR20040080377A (en) 2004-09-18
US20040177903A1 (en) 2004-09-16
CN100554489C (en) 2009-10-28
FR2852330B1 (en) 2007-05-11
DE04290508T1 (en) 2005-03-31
ES2226608T1 (en) 2005-04-01

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