EP0584364A1 - TOLE D'ACIER PLAQUEE Al-Si-Cr, AYANT UNE EXCELLENTE RESISTANCE A LA CORROSION, ET PRODUCTION DE CETTE TOLE - Google Patents

TOLE D'ACIER PLAQUEE Al-Si-Cr, AYANT UNE EXCELLENTE RESISTANCE A LA CORROSION, ET PRODUCTION DE CETTE TOLE Download PDF

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Publication number
EP0584364A1
EP0584364A1 EP93903330A EP93903330A EP0584364A1 EP 0584364 A1 EP0584364 A1 EP 0584364A1 EP 93903330 A EP93903330 A EP 93903330A EP 93903330 A EP93903330 A EP 93903330A EP 0584364 A1 EP0584364 A1 EP 0584364A1
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Prior art keywords
layer
steel
alloy
sheet
sub
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EP93903330A
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German (de)
English (en)
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EP0584364B1 (fr
EP0584364A4 (en
Inventor
Yasushi Nisshin Steel Co. Ltd. Fukui
Tadaaki Miono
Minoru Saito
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Nippon Steel Nisshin Co Ltd
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Nisshin Steel Co Ltd
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Priority claimed from JP4059017A external-priority patent/JPH05222519A/ja
Priority claimed from JP4059016A external-priority patent/JP2938658B2/ja
Priority claimed from JP5034759A external-priority patent/JPH06228725A/ja
Priority claimed from JP03476093A external-priority patent/JP3207958B2/ja
Application filed by Nisshin Steel Co Ltd filed Critical Nisshin Steel Co Ltd
Publication of EP0584364A1 publication Critical patent/EP0584364A1/fr
Publication of EP0584364A4 publication Critical patent/EP0584364A4/en
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/12—Aluminium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/003—Apparatus
    • C23C2/0034—Details related to elements immersed in 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
    • C23C2/0034—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
    • C23C2/003—Apparatus
    • C23C2/0038—Apparatus characterised by the pre-treatment chambers located immediately upstream of the bath or occurring locally before the dipping process
    • C23C2/004—Snouts
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/024—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by cleaning or etching
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/026—Deposition of sublayers, e.g. adhesion layers or pre-applied alloying elements or corrosion protection

Definitions

  • the present invention relates to a hot-dip coated steel sheet remarkably improved in corrosion and heat resistance by the addition of Cr to a hot-dip Al-Si plating layer, and a method for manufacturing said coated steel sheet.
  • An Al-Si alloy-coated steel sheet has been manufactured by introducing a steel sheet into a hot-dip coating bath prepared from an Al-Si alloy.
  • the Al-Si alloy plating layer formed on the surface of the steel sheet is excellent in corrosion and heat resistance and provides a fine surface appearance. These properties of the Al-Si alloy plating layer broadens the use of the coated steel sheet, e.g. parts and members for the exhaust system of an automobile and structural members for building or civil engineering.
  • a conventional hot-dip Al-Si alloy coating method commonly uses a continuous hot-dip coating equipment involving an in-line reducing furnace.
  • a steel sheet to be hot-dip coated is annealed in a reducing atmosphere in a pretreatment zone.
  • the steel sheet is subjected to gas cleaning reaction so that oxide films are reductively removed from the surface of the steel sheet.
  • the surface of the steel sheet is activated.
  • the steel sheet is then introduced into a hot-dip Al-Si alloy coating bath.
  • Japanese Patent Application Laid-Open 2-88754 discloses the use of an Al-Si alloy coating bath containing Cr to let an Al-Si plating layer contain Cr in an amount of 0.01-2 wt.%.
  • the resulting coated steel sheet can be used as a structural material which exhibits sufficient durability even in a severe corrosive atmosphere.
  • the possible amount of Cr to be added to the Al-Si coating bath there is a limitation on the possible amount of Cr to be added to the Al-Si coating bath.
  • Si content is 18 wt.% or less, and the coating bath is held at a temperature of 680 °C or lower.
  • the addition of Cr to be added to the Al-Si coating bath shall be controlled in an amount of 0.5 wt.% or less, so as to prevent the coating bath from rising its temperature too higher.
  • Cr content in an objective Al-Si alloy plating layer could not be increased, and an obtained Al-Si alloy coated steel sheet is not improved so much in corrosion resistance.
  • the kind of a parent sheet is inevitably limited to a steel free of Cr or a low-grade stainless steel containing a small amount of Cr.
  • the corrosion resistance of the Al-Si alloy coated steel sheet could not be substantially improved by the selection of the parent sheet.
  • a steel sheet e.g. a low-alloyed steel or stainless steel, containing an easily oxidizable element such as Cr, Si or Al
  • an easily oxidizable element such as Cr, Si or Al
  • a commonly used in-line reducing process is designed for hot-dip coating common steels, but unappropriate for alloyed steels, stainless steels or the like containing easily oxidizable elements. These elements are easily oxidized and converted to oxide films adherent to the surface of the steel sheet, so that the surface exhibits poor wettability to a hot-dip coating metal.
  • Japanese Patent Publication 63-44825 disclosed another method for improving the corrosion resistance of an Al-Si alloy coated steel sheet.
  • a parent sheet is coated with Ni, Cu, Co or Cr and then processed in a hot-dip Al-Si coating line including a gas cleaning zone.
  • the coated steel sheet obtained in this way is improved in corrosion resistance owing to the precoating of Ni, Cu, Co or Cr.
  • Japanese Patent Publication 63-44825 discloses the use of an Al coating bath containing Si only in an amount of impurity order in addition to maitaining the coating bath at a temperature of approximately 700 °C higher than that of a conventional Al-Si alloy coating bath which is held at 620-670 °C.
  • the reactivity of the coating bath is enhanced effectively for lowering the surface area of uncoated parts by the limitation on Si content and the maintenance of the coating bath at a high temperature.
  • the formation of uncoated parts can not be completely inhibited.
  • oxide films are removed from the surface of the steel sheet by gas cleaning.
  • there are no problems such as those derived from oxide films formed on the Cr-precoated steel sheet.
  • the influence in response to the kind of the precoating layer is suggested in the data disclosed in Japanese Patent Publication 63-44825.
  • the adhesiveness of the Al-Si alloy plating layer to the substrate steel is improved by precoating the parent sheet with Fe or a Fe alloy. Oxide films are easily reductively removed from the surface of the steel sheet, when the precoated parent sheet is passed trough the in-line annealing furnace of a conventional continuous hot-dip coating equipment.
  • Japanese Patent Application Laid-Open 63-176482 discloses the pretreatment wherein a parent sheet is precoated with Co, Ni, Mn, Mo, Cu, Cr and/or W and then with Fe to improve the adhesiveness of an Al plating layer to a substrate steel.
  • the precoating of Fe or a Fe alloy suppresses harmful influence originated in chromium oxide films.
  • the precoating of Fe or a Fe alloy requires an additional step and needs expsenes for electroplating, so that production cost becomes higher in total.
  • the precoated parent sheet is dipped in an hot-dip Al-Si coating bath, the Fe or Fe alloy precoating layer dissolved in the plating layer before its solidification. Consequently, Fe content in the plating layer becomes higher, so that the coated steel sheet obtained in this way is not substantially improved in corrosion resistance.
  • An object of the present invention is to manufacture a steel sheet coated with a superior Al-Si-Cr layer without defects such as uncoated parts or poor adhesiveness derived from chromium oxide films.
  • a superior Al-Si-Cr layer is formed by introducing a parent sheet, on which a Cr coating layer is formed in an active state free from oxide films, into a hot-dip Al-Si alloy copating bath.
  • Another object of the present invention is to obtain a coated steel sheet remarkably improved in corrosion and heat resistance by controlling the conditions of manufacturing to reform the structure of a plating layer.
  • Still another object of the present invention is to produce a steel sheet coated with an Al-Si-Cr plating layer excellent in corrosion and heat resistance with high productivity by arranging the formation of a Cr coating layer and the application of hot-dip Al-Si alloy layer coating in series.
  • a parent sheet on which there is formed a Cr layer having an active surface free of oxide films, is introduced into a hot-dip Al-Si alloy coating bath.
  • a Cr layer is preformed on the surface of the parent sheet by electroplating or vapor deposition.
  • the Cr layer is held in the active state until the Cr coated parent sheet is introduced into the hot-dip coating bath, as follows:
  • the Cr layer may be formed on the surface of a parent sheet by electroplating or vapor deposition.
  • the Cr layer preferably has a thickness of 0.02 ⁇ m or more to improve the corrosion resistance of a product.
  • the parent sheet When the parent sheet is introduced into a hot-dip Al-Si alloy coating bath, Cr diffuses into a plating layer being formed on the surface of the parent sheet. If the Cr layer has a sufficient thickness, the Cr layer remains as an intermediate layer between the substrate steel and the plating layer in the product. If the Cr layer is thin, Cr completely diffuses into the plating layer without remaining at the boundary between the substrate steel and the plating layer.
  • the Cr layer remains between the substrate steel and the plating layer or not depends on the temperature and composition of the hot-dip Al-Si alloy coating bath, a period for dipping the parent sheet in the coating bath, etc. in addition to the thickness of the Cr layer.
  • the coated steel sheet is remarkably improved in corrosion resistance, since the formed plating layer contains Cr.
  • the corrosion resistance is excellent.
  • the plating reaction occurs on the surface of the parent sheet through the Cr layer having a surface activated, so that the formed plating layer exhibits excellent adhesiveness to the substrate steel without the formation of defects such as uncoated parts.
  • the Cr layer effectively suppresses the diffusion of Fe from the substrate steel, the formed plating layer itself is presented with excellent corrosion resistance and workability.
  • the intermediate Cr layer suppresses the alloying reaction between the substrate steel and the plating layer, so as to inhibit the formation of a thick brittle alloyed layer. Consequently, the product is excellent in workability, too.
  • a large amount of Cr may be intentionally diffused into the plating layer to precipitate Cr-Si-Al alloy particles by controlling the hot-dip coating conditions, e.g. holding the hot-dip coating bath at a higher temperature or dipping the parent sheet in the coating bath for a longer time.
  • the precipitation of the Cr-Si-Al alloy particles exhibits a remarkable effect on the improvement in the corrosion resitance of the hot-dip coated steel sheet.
  • the Cr layer Taking into cosideration the above-mentioned effects of the Cr layer, it is preferable to form the Cr layer of 0.1 ⁇ m or more in thickness on the surface of the parent sheet.
  • composition and temperature of the hot-dip coating bath there are not particular restrictions on the composition and temperature of the hot-dip coating bath to be used according to the present invention. However, it is preferable to control Si content within the range of 1-13 wt.% and the temperature of the hot-dip coating bath below 680°C, in order to prolong the life-time of a pot for the coating bath and to enhance the surface appearance of an obtained product. In case where a thin Al-Si-Cr alloy layer is to be formed on the surface of the parent sheet, it is preferable to maintain Si content within the range of 6-12 wt.% and the temperature of the coating bath below 680 °C.
  • the hot-dip coating bath may contain Cr as a third component.
  • Cr as a third component.
  • the use of the Cr-contng. Al-Si alloy coating bath is effective for raising an amount of Cr existent in the plating layer.
  • the amount of Cr to be added to the coating bath which does not limit the scope of the present invention, is 0.5 wt.% or less in the practical point of view. If the coating bath contains an excessive amount of Cr, the coating bath shall be maintained at a higher temperature in response to the elevation of the melting point of the Al-Si alloy.
  • Fe is the element mixed in the biggest amount in the coating bath. Fe concentration in the coating bath is ordinarily controlled at 3 wt.% or less. If the parent sheet is hot-dip coated using the coating bath containing a large amount of Fe under the condition to leave the Cr layer, there would be formed the Fe-contng. Al-Si-Cr alloy layer which unfavorably deteriorates the corrosion resistance of the coated steel sheet.
  • the dissolution of Fe from a structural material such as a pot may be inhibited by applying ceramic lining to the structural material.
  • the dissolution of Fe from the parent sheet into the coating bath is also inhibited, since the parent sheet to be coated is covered with the Cr layer. Consequently, the coating bath is kept at very low Fe concentration, so as to sufficiently lower Fe content in the plating layer to be formed on the surface of the steel sheet.
  • a common steel such as Al-killed steel may be used in order to reduce the cost of a product. Even when a cheap common steel is used as a parent sheet, the obtained product exhibits excellent corrosion resistance similar to that of a high-grade steel material such as stainless steel.
  • the substrate steel When a low-alloyed steel or stainless steel is used as a parent sheet, the substrate steel itself has good corrosion resistance. Owing to the combination of this property with the hot-dip Al-Si coating layer formed on the Cr layer, the coated steel sheet exhibits corrosion and heat resistance superior to those of an expensive high-grade stainless steel containing large amounts of Cr and Ni.
  • Fig. 1 is a schematic view illustrating a plant for continuing plazma etching, vapor Cr deposition and hot-dip coating in the same vacuum chamber according to the present invention.
  • Fig. 2 is a schematic view illustrating a plant for continuing ion beam etching, vapor Cr deposition and hot-dip coating in the same vacuum chamber according to the present invention.
  • Fig. 3 is a schematic view illustrating a plant for continuing vapor Cr deposition, plazma etching and hot-dip coating in the same vacuum chamber according to the present invention.
  • Fig. 4 is a schematic view illustrating a plant for continuing vapor Cr deposition, ion beam etching and hot-dip coating in the same vacuum chamber according to the present invention.
  • Fig. 5 shows the lamellar structure of a plating layer formed according to the present invention.
  • Fig. 6 shows the lamellar structure of another plating layer which contains a large amount of Cr.
  • Fig. 7 is a graph for explaining the effect of the thickness of a Cr layer on Cr content in the second sub-layer of a plating layer and the corrosion resistance of a coated steel sheet obtained in Example 1.
  • Fig. 8 illustrates a plating layer wherein Si-rich alloy particles are precipitated.
  • Fig. 9 is a graph for explaining the effect of the thickness of a Cr layer on Cr content in the second sub-layer of a plating layer and the corrosion resistance of a coated steel sheet obtained in Example 2.
  • Fig. 10 is a graph for explaining the effect of the thickness of a Cr layer on Cr content in the second sub-layer of a plating layer and the corrosion resistance of a coated steel sheet obtained in Example 3.
  • Fig. 11 shows the metallurgical structure and concentration of a plating layer formed on the surface of a steel sheet in Example 5.
  • Fig. 12 is a graph showing the relationship between the thickness of a Cr layer and the corrosion resistance of a coated steel sheet obtained in Example 5.
  • Fig. 13 is a graph for explaining the corrosion resistance of a hot-dip Al-Si alloy-coated steel sheet after being electroplated in comparison with that of the same coated steel sheet after being precoated with Fe.
  • Fig. 14 is a graph for explaining the effects of the thickness of a Cr layer and the temperature of a hot-dip coating bath on the corrosion resistance of a coated steel sheet obtained in Example 6.
  • a parent sheet coated with a Cr layer having a surface activated is introduced into a hot-dip Al-Si coating bath.
  • the Cr layer may be fomed by electroplating or vacuum vapor deposition.
  • the surface of the Cr layer is activated by plazma etching, ion beam etching, etc..
  • the Cr layer keeping its surface in the activated state may be brought into contact with the hot-dip coating bath, when vapor Cr deposition is successively followed by hot-dip coating using a coating bath maintained in the same vacuum chamber.
  • the present invention is realized in various processes classified as follows:
  • a parent sheet 10 is fed out from a pay-off reel 11 and introduced into a vacuum chamber 20, while changing its running direction with deflector rolls 12, 13.
  • a vacuum seal means 21 is provided in the vacuum chamber 20 at its inlet position.
  • a high-frequency heater 30, a vapor Cr deposition device 40 and a plazma etching device 50 are successively aligned along the running direction of the parent sheet 10.
  • the outlet of the vacuum chamber 20 is immersed in a hot-dip coating bath 61 in a hot-dip coating zone 60 to make vacuum sealing at the outlet.
  • the hot-dip coating bath 61 is pumped from a pot 62 up to the height corresponding to the degree of vacuum in the vacuum chamber 20, to form a snout 63.
  • the outlet of the vacuum chamber 20 is completely vacuum sealed by the hot-dip coating bath 61.
  • the vacuum chamber 20 is evacuated by vacuum pumps 22, 23.
  • the parent sheet 10 after being introduced into the vacuum chamber 20 is heated at a predetermined temperature by the high-frequency heater 30, coated with Cr by the vapor Cr deposition device 40 and then activated by the plazma etching device 50.
  • the parent sheet 10 is then introduced through the snout 63 into the hot-dip coating bath 61.
  • the parent sheet 10 is carried along sunk rolls 64, 65 in the hot-dip coating bath 61, and raised from the bath 61.
  • An excessive amount of a coating metal is removed by a gas wiper 66 to control the amount of the coating metal adherent onto the surface of the parent sheet 10.
  • the coated sheet is further carried along deflector rolls 14-16 and then coiled onto a winding reel 17.
  • Fig. 2 shows the layout wherein various devices are arranged in the order of steps in the process 7.
  • a couple of ion beam etching devices 70, 70 are located in the state facing to each surface of the parent sheet 10, instead of the plazma etching device 50 shown in Fig. 1.
  • the surface of the parent sheet 10 is bombarded with ion beams 71, 71 discharged from each ion beam etching device 70, 70.
  • the bombardment of the ion beams 71, 71 induces the etching reaction to remove oxide films and/or denatured surface parts from the Cr layer which has been formed by the vapor Cr deposition device 40.
  • the Cr layer is formed by the vapor Cr deposition device 40 held in the same vacuum atmosphere as that for the hot-dip coating zone 60. Consequently, the Cr layer is maintained under the condition difficult to form oxide films or denatured surface parts, which would impede the adhesion of a coating metal, on the surface of the Cr layer.
  • the plazma etching device 50 or the ion beam etching device 70 may be provided at the downstream of the vapor Cr deposition device 40, when the Cr layer is not suffered from harmful influences such as oxide films.
  • the layout which omits the activating device corresponds to the process 5.
  • Oxide films and/or denatured surface parts are removed from the surface of the Cr layer by plazma etching or ion beam etching.
  • the steel sheet on which the Cr layer is preformed by a device independent from the hot-dip coating equipment may be used as the parent sheet 10.
  • Said Cr layer may be formed by either electroplating or vapor deposition.
  • the process 1 corresponds to the case where the surface of the Cr layer formed by electroplating is activated by plazma etching before the step of hot-dip coating.
  • the process 2 corresponds to the case where the same Cr layer is activated by ion beam etching.
  • the process 3 or 4 is the case where the Cr layer is subjected to plazma etching or ion beam etching, respectively.
  • oxide films and/or denatured layers on the surface of a steel sheet. Said oxide films and/or denatured layers deteriorate the adhesiveness of the Cr layer, to be formed by the vapor Cr deposition device 40, onto the substrate steel.
  • the surface of the steel sheet is preferably activated before the formation of the Cr layer.
  • the process 8 shows the case where ion beam etching is employed for the activating treatment using the layout shown in Fig. 3.
  • the plazma etching device 50 is located at the upstream of the vapor Cr deposition device 40. If necessary, the same plazma etching device may be additionally provided at the downstream of the vapor Cr deposition device 40.
  • the process 9 uses the layout shown in Fig. 4, wherein the surface of the parent sheet 10 is activated by ion beam etching.
  • the ion beam etching device 70 is located at the upstream of the vapor Cr deposition device 40. If necessary, the same ion beam etching device may be additionally provided at the downstream of the vapor Cr deposition device 40.
  • the Cr layer Since the parent sheet 10 coated with the Cr layer having the surface activated is introduced into the coating bath 61, the Cr layer exhibits excellent wettability to the coating metal. Consequently, a fine plating layer is formed on the surface of the steel substrate.
  • the plating layer has the lamellar structure which is changed in resposnse to the operational conditions, e.g. the composition and temperature of the cotaing bath, the thickness of the Cr layer and the kind of the substrate steel.
  • the plating layer has the lamellar structure shown in Fig. 5.
  • the lamellar structure comprises, in the order from the surface of the substrate steel S, the first sub-layer L1 of an Al-Si-Fe alloy, the second sub-layer L2 of an Al-Cr-Si-Fe alloy and the third sub-layer L3 of an Al-Si ally.
  • the second sub-layer L2 is one formed by the diffusion of Cr during dipping the Cr-coated steel sheet in the coating bath.
  • the second sub-layer L2 has the effect to improve corrosion and heat resistance owing to high Cr concentration.
  • the effect of Cr on the corrosion and heat resistance is distinctly noted, when Cr concentration in the second sub-layer L2 is 0.7 wt.% or higher.
  • the Cr concentration is preferably adjusted by controlling the composition and temperature of the coating bath, the thickness of the Cr layer, etc..
  • a conventional hot-dip Al-Si alloy-coated steel sheet does not have a layer corresponding to the second sub-layer L2, but depends on an Al-Si surface layer to protect the substrate steel from corrosion. Consequently, its corrosion resistance is substantially inferior to that of the steel sheet coated with the plating layer including the second sub-layer L2.
  • the Cr content in the second sub-layer L2 has the effect to suppress the diffusion of Fe from the substrate steel S, so as to reduce the total amount of Fe in the plating layer.
  • the plating layer is formed through the Cr layer excellent in adhesiveness and wettability. Consequently, the obtained product is improved in workability as well as corrosion resistance. For instance, the coated steel sheet can be reformed to an objective shape without flaking or powdering.
  • the plating layer obtained under the condition to enhance Cr concentration comprises the first sub-layer L1 of an Al-Si-Fe-Cr alloy, the second sub-layer L2 of an Al-Cr-Si-Fe alloy and the third sub-layer L3 of an Al-Si-Cr alloy.
  • the first sub-layer L1 is excellent in corrosion inhibition, since it contains Cr with high Al concentration. Cr concentration in the first sub-layer L1 is up to 0.7 wt.%, when the plating layer is formed on a parent sheet such as common steel which does not contain Cr. When an alloyed steel or stainless steel is used as a parent sheet, Cr concentration in the first sub-layer L1 is higher owing to the diffusion of Cr from the substrate steel S. The corrosion resistance is more improved, as Cr concentration in the first sub-layer L1 is higher. However, Cr concentration in the first sub-layer L1 does not exceed 5 wt.%, even when a high-Cr steel containing 40 wt.% or more Cr is used as the parent sheet.
  • the second sub-layer L2 is of the Al-Cr-Si-Fe alloy in which Cr is preferentially concentrated.
  • the second sub-layer L2 exhibits the highest effect to inhibit corrosion among the sub-layers L1-L3, since Cr and Al concentrations are both higher.
  • Cr concentration in the second sub-layer L2 is preferably adjusted by controlling the amount of Cr adhering to the parent sheet. For instance, the Cr concentration in the second sub-layer L2 was approximately 3 wt.%, when a Cr layer of 0.1 ⁇ m in thickness was formed on the parent sheet.
  • the thickness of the Cr layer is predetermined taking into consideration the corrosion resistance necessary for the use of a product.
  • the third sub-layer L3 is the Al-Si-Cr alloy layer which is formed by the solidification of a coating metal.
  • the sub-layer L3 has nearly the same composition as that of the coating bath, except Cr.
  • the sub-layer L3 also contains Cr in a small amount of 0.1 wt.% or less due to the diffusion of Cr. Although Cr content is low, the third sub-layer L3 is improved in corrosion inhibition, too.
  • the formed plating layer comprises the first sub-layer L1 of Cr, the second sub-layer L2 of Cr-Si-Al and the third sub-layer L3 of Al-Si-Cr.
  • the second sub-layer L2 promotes the segregation of Fe diffused from the coating bath or the like therein, so as to reduce Fe concentration in the third sub-layer L3.
  • Fe mixed as an impurity in the third sub-layer L3 is preferably controlled in an amount of 0.7 wt.% or less, in order to enhance the effect of the plating layer L to inhibit corrosion reaction.
  • the second sub-layer L2 preferably has the composition of 30-60 wt.% Cr, 30-60 wt.% Si, less than 30 wt.% Fe and the balance being substantially Al
  • the third sub-layer L3 preferably has the composition of 6-12 wt.% Si, 0.05-0.5 wt.% Cr and the balance being substantially Al.
  • the second sub-layer L2 preferably contains 30-60 wt.% Cr with Fe concentration reduced below 30 wt.%, to improve the corrosion resistance by the co-operative effect with the first sub-layer L1.
  • the excessive growth of the second sub-layer L2 would cause the formation of big cracks, when the obtained product is mechanically reformed to a certain shape by bending or the like.
  • Si content in the second sub-layer L2 is preferably controlled at 30-60 wt.% to suppress the growth of the second sub-layer L2.
  • the third sub-layer L3 is excellent in ductility as well as corrosion resistance.
  • the cracks are sealed by the plastic flow of the third sub-layer L3 to prevent the substrate steel from exposing to the atmosphere.
  • Cr content in the third sub-layer L3 is controlled within the range of 0.05-0.5 wt.%, the corrosion resistance is improved without lowering the ductility.
  • the third sub-layer L3 preferably contains 6-12 wt.% Si to improve the coated steel sheet in surface appearance and flatness. Si in the third sub-layer L3 is effective in corrosion inhibition, too.
  • Cr-Si-Al alloy particles G may be dispersed in the third sub-layer L3, as shown in Fig. 6.
  • the dispersion of the alloy particles G further enhances the effect of the third sub-layer L3 to suppress the corrosion reaction.
  • the alloy particles G are those precipitated from the first sub-layer L1 and the second sub-layer L2 by either holding the hot-dip Al-Si alloy coating bath at a higher temperature or dipping the parent sheet in the coating bath for a longer time.
  • the steel sheet hot-dip coated with the Al-Si-Cr plating layer as aforementioned is manufactured by coating a parent sheet with a Cr layer and then introducing the parent sheet into a hot-dip Al-Si alloy coating bath.
  • the Al-Si alloy coating bath does not contain Fe as an impurity
  • the Cr-Si-Al alloy layer is formed as the second sub-layer L2.
  • Fe is mixed as an impurity in the coating bath, Fe is segregated in the second sub-layer L2 during the solidification of the plating layer.
  • a Cr-Si-Al-Fe alloy layer is formed as the second sub-layer L2.
  • a parent sheet to be hot-dip coated was prepared from an Al-killed steel sheet of 0.5 mm in thickness and 100 mm in width.
  • the Al-killed steel had the composition of 0.02 wt.% C, 0.04 wt.% Si, 0.19 wt.% Mn, 0.011 wt.% P, 0.011 wt.% S, 0.045 wt.% Al and the balance being substantially Fe.
  • a vacuum chamber 20 was evacuated to 1 ⁇ 10 ⁇ 3 Pa by vacuum pumps 22, 23. After the interior of the vacuum chamber 20 reached a predetermined degree of vacuum, a high-frequency heater 30, a vapor Cr deposition device 40 and a plazma etching device 50 were put into operation. Hereon, the degree of vacuum in the vacuum chamber 20 was changed to 3 Pa by the introduction of raw gas. Plazma etching was performed under the conditions shown in Table 1. TABLE 1 CONDITIONS FOR PLAZMA ETCHING RAW GAS FOR PLAZMA ETCHING Ar POWER FOR GENERATING PLAZMA 4 kW VOLTAGE CHARGED ON ELECTRODE 350 V FLOW RATE OF RAW GAS 1 ⁇ 10 ⁇ 6 m3/sec. LINE SPEED 30 m/min.
  • the obtained product had a multi-layered alloy plating layer.
  • the third sub-layer L3 in the plating layer was composed of a mixed phase comprising primary crystals of an Al-rich alloy and eutectically precipitated crystals of a Si-rich alloy. Under the third sub-layer L3, there were formed the second sub-layer L2 of Al-Cr-Si-Fe and the first sub-layer L1 of Al-Si-Fe.
  • Cr concentration in the second sub-layer L2 was variously changed by controlling the thickness of a Cr layer to be formed by vacuum deposition, to examine the effect of the thickness of the Cr layer on Cr concentration in the second sub-layer L2 and the corrosion resistance of an obtained product.
  • the results are shown in Fig. 7.
  • corrosion resistance was evaluated as a time period (hereinafter referred to as "5% rust formation time") until the surface area of a test piece was occupied by 5% or more with rust formed on the surface of said test piece in the salt water spray test regulated in JIS (Japanese Industrial Standard).
  • a Cr layer was preformed on the surface of a parent sheet by electroplating, and the parent sheet was introduced into the vacuum chamber 20 of the hot-dip coating plant shown in Fig. 1 or 2.
  • the parent sheet was etched and hot-dip coated with an Al-Si layer.
  • An obtained product was a multi-layered alloy-coated steel sheet which exhibited extremely excellent corrosion resistance as compared with a conventional Al-Si alloy-coated steel sheet, as far as Cr concentration in the second sub-layer L2 was 0.7 wt.% or more.
  • Example 2 The same Al-killed steel as that in Example 1 was used as a parent sheet to be hot-dip coated in the plant shown in Fig. 3.
  • the parent sheet was plazma etched under the conditions shown in Table 1 and then coated with a Cr layer by vacuum deposition. Thereafter, the parent sheet was hot-dip coated under the conditions shown in Table 4.
  • BALANCE Al except inevitable impurities TEMP.
  • the obtained product had a multi-layered alloy plating layer.
  • the third sub-layer L3 in the plating layer was composed of a mixed phase comprising primary crystals of an Al-rich alloy and eutectically precipitated crystals of a Si-rich alloy.
  • test piece was cut out from the coated steel sheet which was obtained by coating a parent sheet with a Cr layer of 0.3 ⁇ m in thickness and then hot-dip coating it in an Al-Si coating bath.
  • the test piece was examined by EPMA linear analysis to investigate the distribution of each element in the plating layer.
  • Fig. 8 shows the result of analysis in comparison with the sectional structure.
  • Cr concentration in the second sub-layer L2 was variously changed by controlling the thickness of a Cr layer to be formed by vacuum deposition.
  • the effect of the Cr layer on corrosion resistance was researched in the same way as that in Example 1. The results are shown in Fig. 9. It is noted from Fig. 9 that the Cr layer of 0.02 ⁇ m or more in thickness effectively improved corrosion resistance. Cr concentration in the second sub-layer L2 was of 0.7 wt.% or more owing to such a thicker Cr layer.
  • the stainless steel SUS410L had the composition of 0.01 wt.% C, 0.48 wt.% Si, 0.23 wt.% Mn, 0.026 wt.% P, 0.003 wt.% S, 11.96 wt.% Cr and the balance being Fe except inevitable impurities.
  • the stainless steel SUS430 had the composition of 0.06 wt.% C, 0.45 wt.% Si, 0.28 wt.% Mn, 0.025 wt.% P, 0.007 wt.% S, 16.44 wt.% Cr and the balance being Fe except inevitable impurities.
  • Each parent sheet was hot-dip coated under all the same conditions as those in Example 2.
  • the combination of Cr coating with a hot-dip coating process was examined to search how to affect the corrosion resistance of an obtained product, as follows:
  • the same Al-killed steel as that in Example 2 was hot-dip coated with an Al-Si alloy layer.
  • the composition of a coating bath and the adhesion amount of a plating layer were adjusted to the same as those in Example 2.
  • the Cr-coated parent sheet was intorduced into the vacuum chamber 20 shown in Fig. 3.
  • the vapor Cr deposition device 50 was not put into operation, but the plazma etching device 40 was operated to activate the surface of the Cr layer. Thereafter, the Cr-coated parent sheet was intorduced into the coating bath.
  • Table 5 shows the corrosion resistance of each product in response to the hot-dip coating process. It is noted from Table 5 that the same excellent corrosion resitance as that in Example 2 is obtained even when hot-dip Al-Si alloy coating was applied to the steel sheet which had been precoated with a Cr layer by vapor deposition or electroplating.
  • Example 2 The same Al-killed steel as that in Example 1 was used as a parent sheet. After the parent sheet was degreased and pickled, a Cr layer was formed on the parent sheet by vapor deposition or electroplating. The Cr-coated parent sheet was hot-dip coated with an Al-Si alloy layer in the plant using the plazma etching device shown in Fig. 3 or the ion beam etching device shown in Fig. 4.
  • the vacuum chamber 20 was evacuated to 1 ⁇ 10 ⁇ 3 Pa by the vacuum pumps 22, 23. After the interior of the vacuum chamber 20 reached a predetermined degree of vacuum, the plazma etching device 50 or the ion beam etching device 70 as well as the high-frequency heater 30 was operated to activate the surface of the parent sheet 10. Hereon, the degree of vacuum in the vacuum chamber 20 was changed to 0.05-5 Pa due to the inflow of raw gas Ar.
  • the parent sheet 10 was heated by the high-frequency heater 30 and conditioned to the state having a surface activated by the plazma etching device 50 or the ion beam etching device 70. Consequently, the Cr layer formed by vapor deposition was uniformly formed on the whole surface of the parent sheet 10 with excellent adhesiveness.
  • plazma etching and ion beam etching were done under the conditions shown in Tables 1 and 3, respectively.
  • the Cr layer remained in the plating layer, even when the parent sheet was immersed in a hot-dip Al-Si allloy coating bath held at a temperature above 640 °C.
  • the formed plating layer had the multi-layered structure shown in Fig. 5 or 6.
  • the coating bath was held at a temperature exceeding 640 °C, Cr-Si-Al alloy particles G were precipitated in the third sub-layer L3.
  • the third sub-layer L3 of the plating layer formed on the surface of a steel substrate was studied in the relationship with the compositions of the hot-dip coating bath.
  • the results are shown in Table 9.
  • the Cr layer shown in Table 9 was formed by vapor deposition, but the same results were obtained as for the Cr layer formed by electroplating.
  • two kinds of coating bathes were used, one having the composition containing 0.08 wt.% Fe as an impurity mixed in the coating bath, and the other having the composition intentionally containing a large amount e.g. 2.11 wt.%, of Fe.
  • a product manufactured from a parent sheet coated with a Cr layer according to the present invention had the third sub-layer, i.e. the outmost layer, of low Fe concentration controlled below 0.62 wt.%, even when the coating bath containing a large amount (2.11 wt.%) of Fe was used for hot-dip coating.
  • the low Fe concentraion is caused by the segregation of Fe in the second sub-layer resulting in the formation of a Cr-Si-Al-Fe alloy layer.
  • the Cr layer formed on the surface of the parent sheet before the hot-dip coating was diffused into the third sub-layer, so that the Cr concentration in the third sub-layer became approximately 0.4 wt.%.
  • the amount of Cr in the third sub-layer means the Cr concentration of the third sub-layer itself except the Cr-Si-Al alloy particles.
  • the third sub-layer exhibits an excellent corrosion inhibiting effect owing to the high Cr concentration and the low Fe concentration in the third sub-layer.
  • the third sub-layer containing 2.0 wt.% or more of Fe regardless the Fe concentration of the coating bath.
  • Such high Fe concentration is caused by the inclusion of Fe in the plating layer from the coating bath as well as the diffusion of Fe from the substrate steel.
  • the third sub-layer was inferior in corrosion inhibition due to the high Fe concentration.
  • Fig.11 shows the result of the analysis in comparison with the metallurgical structure of the plating layer. It is noted in Fig. 11 that the first sub-layer L1 derived from the Cr layer remained on the surface of the substrate steel. Fe, diffused from the coating bath and the substrate steel, was segregated in the second sub-layer L2 composed of a Cr-Si-Al-Fe alloy, while the presence of Fe was not detected in the third sub-layer L3 composed of an Al-Si-Cr alloy. The concentrations of Cr and Si were selectively higher at the part where Cr-Si-Al alloy particles were dispersed in the third sub-layer L3.
  • the metallurgical structure of the coated steel sheet No. 5 was observed by a microscope. It was clearly detected that the plating layer had the multi-layered structure comprising the Cr-contng. first sub-layer L1, the second sub-layer L2 of a Cr-Si-Al alloy and the third sub-layer L3 of an Al-Si-Cr alloy successively formed on the surface of the substrate steel S.
  • the Cr-Si-Al alloy particles were dispersed in the third sub-layer L3.
  • Fig. 12 shows the relationship between the thickness of the Cr layer and corrosion resistance. It is apparent from Fig. 12 that the corrosion resistance was remarkably improved in response to the thickness of the Cr layer especially exceeding 0.1 ⁇ m. The corrosion resistance was further enhanced by the dispersion of the Cr-Si-Al alloy particles in the third sub-layer, when a parent sheet coated with a Cr layer of 2.0 ⁇ m or more in thicknees was immersed in a hot-dip coating bath held at 640°C. The excellent corrosion resistance was not deteriorated by the concentration of Fe included in the second sub-layer.
  • the corrosion resistance of a steel sheet coated with Cr only by vapor deposition was examined for comparison. Even when a thick Cr layer of 8.0 ⁇ m in thickness was formed on the substrate steel, the coated sheet sheel was inferior in corrosion resistance. That is, the 5% rust formation time was shorter than 500 hrs..
  • the excellent corrosion resistance is ensured by keeping the concentration of Cr in the thrid sub-layer. This effect is the same when the Cr-coated steel sheet was activated by ion beam etching.
  • the Cr-coated steel sheet was introduced into the vacuum chamber 20 shown in Fig. 3 or 4, etched and then hot-dip coated in the Al-Si alloy bath.
  • the obtained steel sheet coated with the multi-layered alloy plating layer exhibited excellent corrosion resistance as comapred with a conventional Al-Si alloy-coated steel sheet, as long as the Cr layer was of 0.1 ⁇ m or more in thickness.
  • a product manufactured by hot-dip coating a parent sheet coated with a Cr layer of 0.5 ⁇ m in thickness in any of the process I - VII was excellent in corrosion resistance well over 3500 hrs. by the 5% rust formation time, regardless of the means for forming a Cr layer or the order of the etching and Cr layer-forming steps.
  • a product obtained from a parent sheet coated with a Cr layer of 2.0 ⁇ m in thickness had the 5% rust formation time exceeding 8500 hrs..
  • Fig. 13 shows the effect of Fe concentration in the third sub-layer on corrosion resistance.
  • a parent sheet coated with a Cr layer of 1.5 ⁇ m in thickness was hot-dip coated in an Al-Si alloy coating bath held at 640°C using the plant shown in Fig. 3.
  • Fe content included in the third sub-layer was 0.7 wt.% or lower.
  • a parent sheet was electroplated with a Fe layer and then hot-dip coated in the same way to prepare a test piece for comparative examples wherein Fe content in the third sub-layer was intentionally increased.
  • the Cr layer is also effective in inhibiting the increase of Fe concentration in the third sub-layer.
  • the Cr layer favorably suppresses the increase of Fe concentration in addition to the increase of Cr concentration in the third sub-layer, so as to remarkably improves the corrosion resistance of the coated steel sheet.
  • Parent sheets were coated with an Al-Si alloy plating layer using a Cr-contng. hot-dip coating bath having the composition shown in Table 11.
  • the obtained product had corrosion resistance in the relationship shown in Fig. 14 with the thickness of Cr layers preformed on the surface of the parent sheets.
  • each parent sheet was coated with the Cr layer and then hot-dip coated with the Al-Si alloy plating layer using the plant shown in Fig. 3.
  • the corrosion resistance was examined by the salt water spray test under the same conditions as those in Example 1.
  • HOT-DIP Al-Si COATING BATH COMPOSITION OF HOT-DIP COATING BATH (wt.%)
  • Si 9.2 Fe : 1.7 Cr : 0.13 bal: Al and impurities
  • ADHESION AMOUNT 30 g/m2 per single surface
  • a Cr layer preformed on the surface of a steel sheet to be hot-dip coated serves as a Cr supply source to a plating layer.
  • the steel sheet can be introduced into a hot-dip coating bath under the condition that the Cr layer keeps good wettability to a coating metal, when oxide films formed on the surface of the Cr layer are removed by plazma etching or ion beam etching, or when hot-dip coating continuously follows vapor Cr deposition in the same vacuum chamber.
  • the formed plating layer is effective in corrosion resistance and heat resistance owing to Cr content therein as well as adhesiveness to the steel substrate.
  • the formed plating layers have multi-layered structures each different from the others in response to the thickness of the Cr layers, hot-dip coating conditions, kinds of parent sheets, etc..
  • the coated shteel sheet having any multi-layered structure exhibits excellent corrosion resistance and heat resistance as compared with a conventional hot-dip Al-Si alloy-coated steel sheet.
  • the obtained product will be used as a material in broad industrial fields, e.g. parts and members for the exhaust system of an automobile, and structural sheets for building and civil engineering.

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Abstract

L'invention se rapporte à une tôle d'acier plaquée, ayant des résistances améliorées à la corrosion et à la chaleur, qu'on produit en ajoutant du chrome à une couche de plaquage Al-Si formée sur la surface d'une tôle d'acier par trempage à chaud. La source de chrome utilisée comprend une couche de revêtement en chrome formée sur la surface d'une tôle non plaquée par électrodéposition, par dépôt sous vide, etc. On peut améliorer la mouillabilité de la couche de revêtement en chrome par le métal de plaquage en activant la surface de la couche par attaque au plasma, par attaque au faisceau ionique etc., avant de plonger la tôle d'acier recouverte de chrome dans un bain de trempage à chaud. La couche de plaquage (L) formée sur le substrat en acier (S) comporte une structure stratifiée, constituée par le première couche (L1) à base de chrome, par la seconde couche (L2) à base du système Cr-Al-Si et par la troisième couche (L3) à base du système Al-Si-Cr, lorsque le plaquage est effectué dans des conditions où la couche de revêtement en chrome est épaisse et où la diffusion du chrome est relativement supprimée. Etant donné que la couche de plaquage (L) contient du chrome, la tôle d'acier plaquée qui en résulte présente des résistances à la corrosion et à la chaleur bien meilleures que les tôles d'acier plaquées Al-Si traditionnelles.
EP93903330A 1992-02-12 1993-02-09 TOLE D'ACIER PLAQUEE Al-Si-Cr, AYANT UNE EXCELLENTE RESISTANCE A LA CORROSION, ET PRODUCTION DE CETTE TOLE Expired - Lifetime EP0584364B1 (fr)

Applications Claiming Priority (11)

Application Number Priority Date Filing Date Title
JP59016/92 1992-02-12
JP4059017A JPH05222519A (ja) 1992-02-12 1992-02-12 Ｃｒを含有する溶融めっき鋼板の製造方法
JP4059016A JP2938658B2 (ja) 1992-02-12 1992-02-12 多層合金めっき鋼板及びその製造方法
JP59017/92 1992-02-12
JP7356092 1992-02-25
JP73560/92 1992-02-25
JP5034759A JPH06228725A (ja) 1993-01-29 1993-01-29 溶融Ａｌ−Ｓｉ−Ｃｒ系めっき鋼板及びその製造方法
JP34759/93 1993-01-29
JP03476093A JP3207958B2 (ja) 1992-02-25 1993-01-29 複合Ａｌ合金めっき鋼板及びその製造方法
JP34760/93 1993-01-29
PCT/JP1993/000163 WO1993016210A1 (fr) 1992-02-12 1993-02-09 TOLE D'ACIER PLAQUEE Al-Si-Cr, AYANT UNE EXCELLENTE RESISTANCE A LA CORROSION, ET PRODUCTION DE CETTE TOLE

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EP0584364A1 true EP0584364A1 (fr) 1994-03-02
EP0584364A4 EP0584364A4 (en) 1994-08-17
EP0584364B1 EP0584364B1 (fr) 1996-10-16

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CA (1) CA2107560C (fr)
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EP0760399A1 (fr) * 1995-02-24 1997-03-05 Nisshin Steel Co., Ltd. Tole aluminiee par immersion, son procede de production et dispositif de regulation de la couche d'alliage
WO2020188321A1 (fr) * 2019-03-20 2020-09-24 Arcelormittal Substrat en acier revêtu, procédé de fabrication d'un substrat en acier revêtu, procédé de fabrication d'un produit en acier et produit en acier

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CN103861662B (zh) 2012-12-13 2016-12-21 通用电气公司 带有氧化铝阻隔层的防结焦催化剂涂层

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Publication number Priority date Publication date Assignee Title
EP0760399A1 (fr) * 1995-02-24 1997-03-05 Nisshin Steel Co., Ltd. Tole aluminiee par immersion, son procede de production et dispositif de regulation de la couche d'alliage
EP0760399A4 (fr) * 1995-02-24 2000-04-12 Nisshin Steel Co Ltd Tole aluminiee par immersion, son procede de production et dispositif de regulation de la couche d'alliage
WO2020188321A1 (fr) * 2019-03-20 2020-09-24 Arcelormittal Substrat en acier revêtu, procédé de fabrication d'un substrat en acier revêtu, procédé de fabrication d'un produit en acier et produit en acier
WO2020188529A1 (fr) * 2019-03-20 2020-09-24 Arcelormittal Substrat en acier revêtu, procédé de fabrication d'un substrat en acier revêtu, procédé de fabrication d'un produit en acier et produit en acier

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Publication number Publication date
CA2107560A1 (fr) 1993-08-13
WO1993016210A1 (fr) 1993-08-19
EP0584364B1 (fr) 1996-10-16
EP0584364A4 (en) 1994-08-17
KR0166099B1 (ko) 1999-01-15
CA2107560C (fr) 1999-05-04
DE69305458T2 (de) 1997-03-06
DE69305458D1 (de) 1996-11-21

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