EP0480355B1 - Tôle d'acier revêtue d'un alliage fer-zinc comportant deux couches et possédant une excellente aptitude à la peinture électrolytique et au formage - Google Patents

Tôle d'acier revêtue d'un alliage fer-zinc comportant deux couches et possédant une excellente aptitude à la peinture électrolytique et au formage Download PDF

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Publication number
EP0480355B1
EP0480355B1 EP91117059A EP91117059A EP0480355B1 EP 0480355 B1 EP0480355 B1 EP 0480355B1 EP 91117059 A EP91117059 A EP 91117059A EP 91117059 A EP91117059 A EP 91117059A EP 0480355 B1 EP0480355 B1 EP 0480355B1
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Prior art keywords
iron
zinc alloy
layer
steel sheet
plating
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EP91117059A
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German (de)
English (en)
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EP0480355A3 (en
EP0480355A2 (fr
Inventor
Masaru C/O Nkk Corporation Sagiyama
Masaki C/O Nkk Corporation Abe
Akira C/O Nkk Corporation Hiraya
Junichi C/O Nkk Corporation Inagaki
Masaya C/O Nkk Corporation Morita
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JFE Engineering Corp
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NKK Corp
Nippon Kokan Ltd
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
    • C25D5/10—Electroplating with more than one layer of the same or of different metals
    • 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
    • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
    • C23C28/02—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings only including layers of metallic material
    • C23C28/023—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings only including layers of metallic material only coatings of metal elements only
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/26—After-treatment
    • C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D3/00—Electroplating: Baths therefor
    • C25D3/02—Electroplating: Baths therefor from solutions
    • C25D3/56—Electroplating: Baths therefor from solutions of alloys
    • C25D3/562—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of iron or nickel or cobalt

Definitions

  • the present invention relates to an iron-zinc alloy plated steel sheet having two plating layers and excellent in electropaintability and press-formability.
  • An iron-zinc alloy plated steel sheet has many advantages such as excellent corrosion resistance and electropaintability and a low manufacturing cost, so that the iron-zinc alloy plated steel sheet is widely used as a steel sheet for an automobile body. There is a strong demand for the improvement of electropaintability and press-formability of such an iron-zinc alloy plated steel sheet.
  • a paint film is formed on the surface of an iron-zinc alloy plated steel sheet usually as follows: Subjecting the iron-zinc alloy plated steel sheet to a phosphating treatment to form a phosphate film on the surface of the iron-zinc alloy plating layer, and then subjecting same to a cation-type electropainting treatment to form a paint film having a prescribed thickness on the phosphate film.
  • Japanese Patent Publication No. 58-15,554 dated March 26, 1983 discloses an iron-zinc alloy plated steel sheet for a cation-type electropainting, having two plating layers, which comprises: a steel sheet; an iron-zinc alloy plating layer as a lower layer formed on at least one surface of said steel sheet, the zinc content in said iron-zinc alloy plating layer as the lower layer being over 40 wt.% relative to said iron-zinc alloy plating layer as the lower layer; and an iron-zinc alloy plating layer as an upper layer formed on said iron-zinc alloy plating layer as the lower layer, the zinc content in said iron-zinc alloy plating layer as the upper layer being up to 40 wt.% relative to said iron-zinc alloy plating layer as the upper layer (hereinafter referred to as the "prior art 1").
  • the iron-zinc alloy plated steel sheet for an automobile body is subjected to a severe press-forming.
  • the severe press-forming applied to the iron-zinc alloy plated steel sheet causes a powdery peeloff of the iron-zinc alloy plating layer, known as the "powdering” and a flaky peeloff of the iron-zinc alloy plating layer, known as the "flaking".
  • Japanese Patent Provisional Publication No. 2-66,148 dated March 6, 1990 discloses an iron-zinc alloy plated steel sheet having two plating layers and excellent in powdering resistance and flaking resistance, which comprises: a steel sheet; an iron-zinc alloy plating layer as a lower layer formed on at least one surface of said steel sheet, the iron content in said iron-zinc alloy plating layer as the lower layer being up to 12 wt.% relative to said iron-zinc alloy plating layer as the lower layer; and an iron-zinc alloy plating layer as an upper layer formed on said iron-zinc alloy plating layer as the lower layer, the iron content in said iron-zinc alloy plating layer as the upper layer being at least 50 wt.% relative to said iron-zinc alloy plating layer as the upper layer, and the frictional coefficient of said iron-zinc alloy plating layer as the upper layer being up to 0.22 (hereinafter referred to as the "prior art 2").
  • the prior arts 1 and 2 have the following problems: Application of a severe press-forming to the iron-zinc alloy plated steel sheet of the prior art 1 or 2 causes the production of cracks or peeloffs in the alloying-treated iron-zinc alloy dip-plating layer as the lower layer and the iron-zinc alloy electroplating layer as the upper layer.
  • An object of the present invention is therefore to provide an iron-zinc alloy plated steel sheet having two plating layers, in which such defects as bubbles and pinholes do not occur in the paint film even when subjected to a severe press-forming, and which is excellent in electropaintability and press-formability.
  • an iron-zinc alloy plated steel sheet having two plating layers and excellent in electropaintability and press-formability which comprises: a steel sheet; an alloying-treated iron-zinc alloy dip-plating layer as a lower layer, formed on at least one surface of said steel sheet, the iron content in said iron-zinc alloy dip-plating layer as the lower layer being within a range of from 7 to 15 wt.% relative to said iron-zinc alloy dip-plating layer, and the plating weight of said iron-zinc alloy dip-plating layer as the lower layer being within a range of from 30 to 120 g/m2 per surface of said steel sheet; and an iron-zinc alloy electroplating layer as an upper layer, formed on said alloying-treated iron-zinc alloy dip-plating layer as the lower layer, the iron content in said iron-zinc alloy electro-plating layer as the upper layer being at least 60 wt.% relative to said iron-zinc alloy electroplating layer;
  • an iron-zinc alloy plated steel sheet having two plating layers and excellent in electopaintability and press-formability which comprises: a steel sheet; an alloying-treated iron-zinc alloy dip-plating layer as a lower layer, formed on at least one surface of said steel sheet, the iron content in said iron-zinc alloy dip-plating layer as the lower layer being within a range of from 7 to 15 wt.% relative to said iron-zinc alloy dip-plating layer, and the plating weight of said iron-zinc alloy dip-plating layer as the lower layer being within a range of from 30 to 120 g/m2 per surface of said steel sheet; and an iron-zinc alloy electroplating layer as an upper layer, formed on said alloying-treated iron-zinc alloy dip-plating layer as the lower layer, the iron content in said iron-zinc alloy electroplating layer as the upper layer being at least 60 wt.% relative to said iron-zinc alloy electroplating layer;
  • the iron-zinc alloy electroplating layer as the upper layer which is formed through the electro-precipitation of metals, has a considerable inner stress therein.
  • the alloying-treated iron-zinc alloy dip-plating layer as the lower layer has almost no inner stress therein. Consequently, the iron-zinc alloy electroplating layer as the upper layer locally and strongly restrains the alloying-treated iron-zinc alloy dip-plating layer as the lower layer.
  • cracks or peeloffs tend to occur in the alloying-treated iron-zinc alloy dip-plating layer as the lower layer.
  • bubbles are produced in the paint film resulting from the vaporization of crystal water released from the phosphate crystal grains of the phosphate film, as described above.
  • the present invention was made on the basis of the above-mentioned findings.
  • the iron-zinc alloy plated steel sheet of the present invention having two plating layers and excellent in electropaintability and press-formability, is described below with reference to the drawings.
  • Fig. 1 is a diagrammatic plan view illustrating a first embodiment of the iron-zinc alloy plated steel sheet of the present invention
  • Fig. 2 is a diagrammatic vertical sectional view illustrating the first embodiment of the iron-zinc alloy plated steel sheet of the present invention.
  • the iron-zinc alloy plated steel sheet of the first embodiment of the present invention comprises a steel sheet 1, an alloying-treated iron-zinc alloy dip-plating layer 2 as a lower layer formed on at least one surface of the steel sheet 1, and an iron-zinc alloy electroplating layer 3 as an upper layer formed on the iron-zinc alloy dip-plating layer 2 as the lower layer, and the iron-zinc alloy electroplating layer 3 as the upper layer has a plurality of dots of another iron-zinc alloy 3a.
  • the iron content in the alloying-treated iron-zinc alloy dip-plating layer 2 as the lower layer should be limited within a range of from 7 to 15 wt.% relative to the iron-zinc alloy dip-plating layer 2.
  • the iron content in the iron-zinc alloy dip-plating layer 2 as the lower layer is under 7 wt.% relative to the iron-zinc alloy dip-plating layer 2, corrosion resistance of the iron-zinc alloy dip-plating layer 2 is degraded.
  • the iron content in the iron-zinc alloy dip-plating layer 2 as the lower layer is over 15 wt.% relative to the iron-zinc alloy dip-plating layer 2, on the other hand, press-formability of the iron-zinc alloy plated steel sheet is degraded.
  • the plating weight of the alloying-treated iron-zinc alloy dip-plating layer 2 as the lower layer should be limited within a range of from 30 to 120 g/m2 per surface of the steel sheet 1.
  • the plating weight of the iron-zinc alloy dip-plating layer 2 as the lower layer is under 30 g/m2 per surface of the steel sheet 1, corrosion resistance of the iron-zinc alloy dip-plating layer 2 is degraded.
  • the plating weight of the iron-zinc alloy dip-plating layer 2 as the lower layer is over 120 g/m2 per surface of the steel sheet, on the other hand, press-formability of the iron-zinc alloy plated steel sheet is degraded.
  • the iron content in the iron-zinc alloy electroplating layer 3 as the upper layer should be limited to at least 60 wt.% relative to the iron-zinc alloy electroplating layer 3.
  • the iron content in each of the plurality of dots of another iron-zinc alloy 3a present in the iron-zinc alloy electroplating layer 3 as the upper layer should be limited to under 60 wt.% relative to each of the plurality of dots of another iron-zinc alloy 3a.
  • the iron-zinc alloy electroplating layer 3 as the upper layer has the plurality of dots of another iron-zinc alloy 3a as described above.
  • the structure of the iron-zinc alloy electroplating layer 3 as the upper layer is therefore non-uniform. Consequently, the inner stress in the iron-zinc alloy electroplating layer 3 as the upper layer is dispersed, and thus the restraining force acting on the alloying-treated iron-zinc alloy dip-plating layer 2 as the lower layer is reduced. Even when a severe press-forming is applied to the iron-zinc alloy plated steel sheet having these two plating layers, therefore, cracks or peeloffs never occur in the alloying-treated iron-zinc alloy dip-plating layer 2 as the lower layer. As a result, bubbles are never produced in the paint film formed on the surface of the iron-zinc alloy electroplating layer 3 as the upper layer.
  • the total exposed area per unit area of the plurality of dots of another iron-zinc alloy 3a present in the iron-zinc alloy electroplating layer 3 as the upper layer should be limited within a range of from 5 to 50% of the unit area of the iron-zinc alloy electroplating layer 3.
  • the total exposed area of the plurality of dots of another iron-zinc alloy 3a is under 5% of the unit area of the iron-zinc alloy electroplating layer 3, the inner stress in the iron-zinc alloy electroplating layer 3 cannot be fully dispersed.
  • the diameter of each of the plurality of dots of another iron-zinc alloy 3a present in the iron-zinc alloy electroplating layer 3 as the upper layer should be limited within a range of from 1 to 100 »m.
  • the diameter of each of the plurality of dots of another iron-zinc alloy 3a is under 1 »m, the inner stress in the iron-zinc alloy electroplating layer 3 cannot be fully dispersed. It is therefore impossible to reduce the restraining force acting on the alloying-treated iron-zinc alloy dip-plating layer 2 as the lower layer, and thus to prevent the production of the cracks or the peeloffs in the iron-zinc alloy dip-plating layer 2 during the press-forming.
  • the diameter of each of the plurality of dots of another iron-zinc alloy 3a is over 100 »m, on the other hand, crater-shaped pinholes tend to occur in the paint film formed on the surface of the iron-zinc alloy electroplating layer 3.
  • the total plating weight of the iron-zinc alloy electroplating layer 3 as the upper layer and the plurality of dots of another iron-zinc alloy 3a should be limited within a range of from 1 to 10 g/m2 per surface of the steel sheet 1. With a total plating weight of under 1 g/m2 per surface of the steel sheet 1, crater-shaped pinholes tend to occur in the paint film formed on the surface of the iron-zinc alloy electroplating layer 3 as the upper layer. With a total plating weight of over 10 g/m2 per surface of the steel sheet 1, on the other hand, press-formability of the iron-zinc alloy plated steel sheet is degraded.
  • Fig. 3 is a diagrammatic plan view illustrating a second embodiment of the iron-zinc alloy plated steel sheet of the present invention
  • Fig. 4 is a diagrammatic vertical sectional view illustrating the second embodiment of the iron-zinc alloy plated steel sheet of the present invention.
  • the iron-zinc alloy plated steel sheet of the second embodiment of the present invention comprises a steel sheet 1, an alloying-treated iron-zinc alloy dip-plating layer 2 as a lower layer formed on at least one surface of the steel sheet 1, and an iron-zinc alloy electroplating layer 4 as an upper layer formed on the iron-zinc alloy dip-plating layer 2 as the lower layer, and the iron-zinc alloy electroplating layer 4 as the upper layer has a plurality of pores 4a.
  • the iron content in the alloying-treated iron-zinc alloy dip-plating layer 2 as the lower layer should be limited within a range of from 7 to 15 wt.% relative to the iron-zinc alloy dip-plating layer 2, and the plating weight of the alloying-treated iron-zinc alloy dip-plating layer 2 as the lower layer should be limited within a range of from 30 to 120 g/m2, under the same reasons just as those in the iron-zinc alloy plated steel sheet of the first embodiment of the present invention.
  • the iron content in the iron-zinc alloy electroplating layer 4 as the upper layer should be limited to at least 60 wt.% relative to the iron-zinc alloy electroplating layer 4.
  • the iron-zinc alloy electroplating layer 4 as the upper layer has the plurality of pores 4a as described above.
  • the structure of the iron-zinc alloy electroplating layer 4 as the upper layer is therefore non-uniform. Consequently, the inner stress in the iron-zinc alloy electroplating layer 4 as the upper layer is dispersed, and thus the restraining force acting on the alloying-treated iron-zinc alloy dip-plating layer 2 as the lower layer is reduced.
  • the total opening area per unit area of the plurality of pores 4a present in the iron-zinc alloy electroplating layer 4 as the upper layer should be limited within a range of from 5 to 50% of the unit area of the iron-zinc alloy electroplating layer 4.
  • the total opening area of the plurality of pores 4a is under 5% of the unit area of the iron-zinc alloy electroplating layer 4, the inner stress in the iron-zinc alloy electroplating layer 4 cannot be fully dispersed. It is therefore impossible to reduce the restraining force acting on the alloying-treated iron-zinc alloy dip-plating layer 2 as the lower layer, and thus to prevent the production of the cracks or the peeloffs in the iron-zinc alloy dip-plating layer 2 during the press-forming.
  • the diameter of each of the plurality of pores 4a present in the iron-zinc alloy electroplating layer 4 as the upper layer should be limited within a range of from 1 to 100 »m.
  • the diameter of each of the plurality of pores 4a is under 1 »m, the inner stress in the iron-zinc alloy electroplating layer 4 cannot be fully dispersed. It it therefore impossible to reduce the restraining force acting on the alloying-treated iron-zinc alloy dip-plating layer 2 as the lower layer, and thus to prevent the production of the cracks or the peeloffs in the iron-zinc alloy dip-plating layer 2 during the press-forming.
  • the diameter of each of the plurality of pores 4a is over 100 »m, on the other hand, crater-shaped pinholes tend to occur in the paint film formed on the surface of the iron-zinc alloy electroplating layer 4.
  • the plating weight of the iron-zinc alloy electroplating layer 4 as the upper layer should be limited within a range of from 1 to 10 g/m2 per surface of the steel sheet 1.
  • the plating weight of the iron-zinc alloy electroplating layer 4 is under 1 g/m2 per surface of the steel sheet 1, crater-shaped pinholes tend to occur in the paint film formed on the surface of the iron-zinc alloy electroplating layer 4 as the upper layer.
  • the plating weight of the iron-zinc alloy electroplating layer 4 is over 10 g/m2 per surface of the steel sheet 1, on the other hand, press-formability of the iron-zinc alloy plated steel sheet is degraded.
  • the iron-zinc alloy plated steel sheet of the present invention having two plating layers and excellent in electropaintability and press-formability is manufactured as follows.
  • a steel sheet is passed through a zinc dip-plating bath to apply a zinc dip-plating treatment to the steel sheet to form a zinc plating layer on at least one surface of the steel sheet. Then, the zinc plated steel sheet is heated to alloy the zinc plating layer and the surface portion of the steel sheet together to convert the zinc plating layer into an iron-zinc alloy plating layer.
  • the alloying-treated iron-zinc alloy dip-plating layer as a lower layer is thus formed on at least one surface of the steel sheet.
  • the heating of the zinc plated steel sheet for the alloying treatment is carried out at a temperature within a range of from 420 to 520°C, which is lower than the usual heating temperature for the alloying treatment.
  • columnar crystal grains ( ⁇ -phase) are produced in the alloying-treated iron-zinc alloy dip-plating layer, so that fine irregularities are formed on the surface of the iron-zinc alloy dip-plating layer.
  • the steel sheet on the surface of which the iron-zinc alloy dip-plating layer having these fine irregularities has been formed is subjected to a temper rolling to level the convexities of the surface of the iron-zinc alloy dip-plating layer.
  • An alloying-treated iron-zinc alloy dip-plating layer having fine concavities is thus formed as a lower layer on at least one surface of the steel sheet.
  • the steel sheet on the surface of which the alloying-treated iron-zinc alloy dip-plating layer having fine concavities has been formed is electroplated with a prescribed electric current density in an acidic electroplating bath containing iron ions in a prescribed amount and zinc ions in a prescribed amount to form an iron-zinc alloy electroplating layer as an upper layer on the alloying-treated iron-zinc alloy dip-plating layer having fine concavities as the lower layer.
  • the iron-zinc alloy plated sheet of the first embodiment of the present invention as shown in Figs. 1 and 2, having two plating layers which comprises the alloying-treated iron-zinc alloy dip-plating layer 2 as the lower layer formed on at least one surface of the steel sheet 1, and the iron-zinc alloy electroplating layer 3 as the upper layer formed on the iron-zinc alloy dip-plating layer 2 as the lower layer and having the plurality of dots of another iron-zinc alloy 3a, or there is manufactured the iron-zinc alloy plated steel sheet of the second embodiment of the present invention as shown in Figs.
  • Which of the iron-zinc alloy plated steel sheet of the first embodiment of the present invention and the iron-zinc alloy plated steel sheet of the second embodiment of the present invention is manufactured depends upon the plating electric current density applied when forming the iron-zinc alloy electroplating layer 3 or 4 as the upper layer on the alloying-treated iron-zinc alloy dip-plating layer 2 as the lower layer and the quantity of the columnar crystal grains produced in the alloying-treated iron-zinc alloy dip-plating layer 2.
  • the iron content in the iron-zinc alloy electroplating layer 3 or 4 as the upper layer and the plating weight of the iron-zinc alloy electroplating layer 3 or 4 as the upper layer depend upon the chemical composition of the electroplating bath and the plating electric current density applied when forming the iron-zinc alloy electroplating layer 3 or 4.
  • the iron content, the diameter, and the total exposed area of the plurality of dots of another iron-zinc alloy 3a present in the iron-zinc alloy electroplating layer 3 as the upper layer depend upon the quantity of the columnar crystal grains produced in the alloying-treated iron-zinc alloy dip-plating layer 2 as the lower layer, the reduction rate of the temper rolling of the steel sheet 1 on the surface of which the iron-zinc alloy dip-plating layer 2 has been formed, and the plating electric current density applied when forming the iron-zinc alloy electroplating layer 3 as the upper layer.
  • the diameter and the total opening area of the plurality of pores 4a present in the iron-zinc alloy electroplating layer 4 as the upper layer also depend upon the quantity of the columnar crystal grains produced in the alloying-treated iron-zinc alloy dip-plating layer 2 as the lower layer, the reduction rate of the temper rolling of the steel sheet 1 on the surface of which the iron-zinc alloy dip-plating layer 2 has been formed, and the plating electric current density applied when forming the iron-zinc alloy electroplating layer 4 as the upper layer.
  • the iron content in the alloying-treated iron-zinc alloy dip-plating layer 2 as the lower layer, and the plating weight of the iron-zinc alloy dip-plating layer 2 depend upon the chemical composition and the temperature of the zinc dip-plating bath used when forming the alloying-treated iron-zinc alloy dip-plating layer 2 as the lower layer on at least one surface of the steel sheet 1, the temperature of the steel sheet 1 passing through the zinc dip-plating bath, the alloying treatment temperature for alloying the zinc plating layer and the surface portion of the steel sheet 1 together, and the period of time for the alloying treatment.
  • the method for manufacturing the iron-zinc alloy plated steel sheet of the present invention is not limited to the above-mentioned one.
  • iron-zinc alloy plated steel sheet of the present invention having two plating layers and excellent in electropaintability and press-formability, is described below further in detail by means of examples while comparing with examples for comparison.
  • each of cold-rolled steel sheets having a thickness of 0.8 mm were cleaned by means of a usual alkali degreasing and a usual electrolytic pickling. Then, the thus cleaned cold-rolled steel sheet was subjected to an alloying-treated iron-zinc alloy dip-plating under any one of three kinds of plating conditions A, B and C as shown in Table 1 to form an alloying-treated iron-zinc alloy dip-plating layer as a lower layer on each of the both surfaces of the cold-rolled steel sheet.
  • the cold-rolled steel sheet on each surface of which the alloying-treated iron-zinc alloy dip-plating layers as the lower layers had been formed was electroplated under any of five kinds of plating conditions a, b, c, d and e as shown in Table 2 to form an iron-zinc alloy electroplating layer as an upper layer on the iron-zinc alloy dip-plating layer.
  • Each sample was subjected to an immersion-type phosphating treatment in a phosphating solution to form a phosphate film on each of the both surfaces of each sample, then subjected to a cation-type electropainting treatment to form a paint film having a thickness of 20 »m on each phosphate film under the following conditions: Impressed voltage 260 V, Paint temperature 27°C, Ratio of sample surface/anode surface 1/1, Baking temperature 270°C, and Baking time 10 minutes.
  • Each sample was subjected to an immersion-type phosphating treatment in a phosphating solution to form a phosphate film on each of the both surfaces of each sample, and then subjected to a cation-type electropainting treatment to form paint film having a thickness of 20 »m on the phosphate film under the following conditions: Impressed voltage 280 V, Paint temperature 27°C, Ratio of sample surface/anode surface 1/1, Baking temperature 170°C, and Baking time 25 minutes.
  • the draw-bead tester comprises a male die 5 having a substantially horizontal projection 6 with a prescribed height, and a female die 7 having a groove 8 with a prescribed depth facing the projection 6 of the male die 5. While the male die 5 is stationarily secured, the female die 7 is horizontally movable toward the male die 5 by means of a hydraulic cylinder not shown.
  • a tip 6a of the projection 6 of the male die 5 has a radius of 0.5 mm.
  • a shoulder 8a of the groove 8 of the female die 7 has a radius of 1 mm.
  • the projection 6 of the male die 5 and the groove 8 of the female die 7 have a width of 40 mm.
  • test piece 9 (i.e., each of the samples of the invention Nos. 1 to 20 and the samples for comparison Nos. 1 to 8) having a width of 30 mm was vertically inserted into the gap between the male die 5 and the female die 7 of the above-mentioned draw-bead tester, and by operating the hydraulic cylinder not shown, the test piece 9 was pressed against the projection 6 of the male die 5 and the shoulders 8a of the groove 8 of the female die 7 under a pressure of 500 Kgf/cm2 (49 MPa). Then, the test piece 9 was pulled out upward as shown by the arrow in Fig. 5 to squeeze same.
  • the sample for comparison No. 1 in which the iron content in the iron-zinc alloy electroplating layer as the upper layer was low outside the scope of the present invention, showed the production of many crater-shaped pinholes in the paint film, resulting in a poor electropaintability.
  • the sample for comparison No. 2 in which the iron content in each of the plurality of dots of another iron-zinc alloy present in the iron-zinc alloy electroplating layer as the upper layer was high outside the scope of the present invention, showed the production of many bubbles in the paint film, revealing a low electropaintability.
  • the sample for comparison No. 3 in which the total exposed area per unit area of the plurality of dots of another iron-zinc alloy present in the iron-zinc alloy electroplating layer as the upper layer was small outside the scope of the present invention, showed the production of many bubbles in the paint film, leading to a low electropaintability.
  • the sample for comparison No. 4 in which the total exposed area per unit area of the plurality of dots of another iron-zinc alloy was large outside the scope of the present invention, showed the production of many crater-shaped pinholes in the paint film, revealing a low electropaintability.
  • the sample for comparison No. 5 in which the diameter of each of the plurality of dots of another iron-zinc alloy present in the iron-zinc alloy electroplating layer as the upper layer was small outside the scope of the present invention, showed the production of many bubbles in the paint film, resulting in a low electropaintability.
  • the sample for comparison No. 6 in which the diameter of each of the plurality of dots of another iron-zinc alloy was large outside the scope of the present invention, showed the production of many crater-shaped pinholes in the paint film, revealing a low electropaintability.
  • the sample for comparison No. 7 in which the total plating weight of the iron-zinc alloy electroplating layer as the upper layer and the plurality of dots of another iron-zinc alloy was small outside the scope of the present invention, showed the production of many crater-shaped pinholes in the paint film, leading to a low electropaintability.
  • the sample for comparison No. 8 in which the above-mentioned total plating weight was large outside the scope of the present invention, showed the production of many bubbles in the paint film, thus revealing a low electropaintability, and showed a poor press-formability.
  • an iron-zinc alloy plated steel sheet having two plating layers in which such defects as bubbles and pinholes do not occur in the paint film even when subjected to a severe press-forming, and which is excellent in electropaintability and press-formability, thus providing industrially useful effects.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Mechanical Engineering (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Thermal Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Electrochemistry (AREA)
  • Electroplating Methods And Accessories (AREA)
  • Coating With Molten Metal (AREA)
  • Electroplating And Plating Baths Therefor (AREA)

Claims (2)

  1. Une tôle d'acier revêtue d'un alliage fer-zinc comportant deux couches de placage et possédant une excellente aptitude à la peinture électrolytique et au formage à la presse, qui comporte :
       une tôle d'acier ;
       comme couche intérieure, une couche de placage par trempage d'alliage fer-zinc traitée par alliage, formée sur au moins une surface de ladite tôle d'acier, la teneur en fer de ladite couche de placage par trempage d'alliage fer-zinc, en tant que couche inférieure, étant située dans la plage de 7 à 15 % en poids par rapport à ladite couche de placage par trempage en alliage fer-zinc, et le poids de placage de ladite couche de placage par trempage en alliage fer-zinc, en tant que couche inférieure, étant situé dans une plage de 30 à 120 g/m² de la surface de ladite tôle d'acier ; et
       comme couche supérieure, une couche d'électroplacage en alliage fer-zinc, formée sur ladite couche de placage par trempage en alliage fer-zinc traitée par alliage, la teneur en fer de ladite couche d'électroplacage en alliage fer-zinc, en tant que couche supérieure, étant d'au moins 60 % en poids par rapport à ladite couche d'électroplacage en alliage fer-zinc ;
       caractérisée en ce que :
       ladite couche d'électroplacage en alliage fer-zinc, en tant que couche supérieure, comporte une pluralité de points d'un autre alliage fer-zinc ;
       la teneur en fer dans chacun de ladite pluralité de points de l'autre alliage fer-zinc est inférieure à 60 % en poids par rapport à chacun de ladite pluralité de points de l'autre alliage fer-zinc ;
       l'aire totale exposée par unité de surface de ladite pluralité de points de l'autre alliage fer-zinc est située dans la plage de 5 à 50 % de l'aire unitaire de ladite couche d'électroplacage en alliage fer-zinc en tant que couche supérieure;
       chacun de ladite pluralité de points de l'autre alliage fer-zinc présente un diamètre situé dans la plage de 1 à 100 »m; et
       le poids total de placage de ladite couche d'électroplacage en alliage fer-zinc, en tant que couche supérieure, et de ladite pluralité de points de l'autre alliage fer-zinc est situé dans la plage de 1 à 10 g/m² de surface de ladite tôle d'acier.
  2. Une tôle d'acier revêtue d'un alliage fer-zinc comportant deux couches de placage et possédant une excellente aptitude à la peinture électrolytique et au formage à la presse, qui comporte :
       une tôle d'acier ;
       comme couche intérieure, une couche de placage par trempage d'alliage fer-zinc traitée par alliage, formée sur au moins une surface de ladite tôle d'acier, la teneur en fer de ladite couche de placage par trempage d'alliage fer-zinc, en tant que couche inférieure, étant située dans la plage de 7 à 15 % en poids par rapport à ladite couche de placage par trempage en alliage fer-zinc, et le poids de placage de ladite couche de placage par trempage en alliage fer-zinc, en tant que couche inférieure, étant situé dans une plage de 30 à 120 g/m² de la surface de ladite tôle d'acier ; et
       comme couche supérieure, une couche d'électroplacage en alliage fer-zinc, formée sur ladite couche de placage par trempage en alliage fer-zinc traitée par alliage, la teneur en fer de ladite couche d'électroplacage en alliage fer-zinc, en tant que couche supérieure, étant d'au moins 60 % en poids par rapport à ladite couche d'électroplacage en alliage fer-zinc ;
       caractérisée en ce que :
       ladite couche d'électroplacage en alliage fer-zinc, en tant que couche supérieure, présente une pluralité de pores ;
       l'aire totale des ouvertures par unité de surface de ladite pluralité de pores est située dans la plage de 5 à 50 % de l'aire unitaire de ladite couche d'électroplacage en alliage fer-zinc, en tant que couche supérieure ;
       chacun de ladite pluralité de pores présente un diamètre situé dans la plage de 1 à 100 »m ; et
       le poids de placage de ladite couche d'électroplacage en alliage fer-zinc, en tant que couche supérieure, est situé dans la plage de 1 à 10 g/m² de surface de ladite tôle d'acier.
EP91117059A 1990-10-08 1991-10-07 Tôle d'acier revêtue d'un alliage fer-zinc comportant deux couches et possédant une excellente aptitude à la peinture électrolytique et au formage Expired - Lifetime EP0480355B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2270171A JP2536271B2 (ja) 1990-10-08 1990-10-08 電着塗装性および加工性に優れた、複数の鉄―亜鉛合金めっき層を有する鉄―亜鉛合金めっき鋼板
JP270171/90 1990-10-08

Publications (3)

Publication Number Publication Date
EP0480355A2 EP0480355A2 (fr) 1992-04-15
EP0480355A3 EP0480355A3 (en) 1992-09-02
EP0480355B1 true EP0480355B1 (fr) 1995-02-08

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EP91117059A Expired - Lifetime EP0480355B1 (fr) 1990-10-08 1991-10-07 Tôle d'acier revêtue d'un alliage fer-zinc comportant deux couches et possédant une excellente aptitude à la peinture électrolytique et au formage

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EP (1) EP0480355B1 (fr)
JP (1) JP2536271B2 (fr)
KR (1) KR920008223A (fr)
CA (1) CA2052112C (fr)
DE (1) DE69107270T2 (fr)

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GB2320033B (en) 1996-12-05 2001-06-06 Fmc Corp Improvements in strength and wear resistance of mechanical components
KR100349153B1 (ko) * 1997-12-26 2002-11-18 주식회사 포스코 전기도금장치및이를이용한강판의밴드자국제거방법

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4329402A (en) * 1978-09-27 1982-05-11 Whyco Chromium Co., Inc. Micro-throwing alloy undercoatings and method for improving corrosion resistance
JPS6056090A (ja) * 1983-09-07 1985-04-01 Kobe Steel Ltd 耐塗膜剥離性に優れためっき鋼板
JPH02145778A (ja) * 1988-11-28 1990-06-05 Kobe Steel Ltd 合金化溶融亜鉛めつき鋼板へのＺｎ−Ｆｅフラツシュめつき方法

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JP2536271B2 (ja) 1996-09-18
CA2052112C (fr) 1997-09-09
EP0480355A3 (en) 1992-09-02
JPH04147992A (ja) 1992-05-21
KR920008223A (ko) 1992-05-27
CA2052112A1 (fr) 1992-04-09
EP0480355A2 (fr) 1992-04-15
DE69107270T2 (de) 1995-07-13
DE69107270D1 (de) 1995-03-23

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