EP0342585B1 - Beschichtete Stahlbleche und Verfahren zu deren Herstellung - Google Patents

Beschichtete Stahlbleche und Verfahren zu deren Herstellung Download PDF

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EP0342585B1
EP0342585B1 EP89108750A EP89108750A EP0342585B1 EP 0342585 B1 EP0342585 B1 EP 0342585B1 EP 89108750 A EP89108750 A EP 89108750A EP 89108750 A EP89108750 A EP 89108750A EP 0342585 B1 EP0342585 B1 EP 0342585B1
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Prior art keywords
coating
weight
corrosion resistance
coated steel
steel sheet
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English (en)
French (fr)
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EP0342585A1 (de
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Yoshio C/O Nippon Steel Corporation Shindou
Fumio C/O Nippon Steel Corporation Yamazaki
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Nippon Steel Corp
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Nippon Steel Corp
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Priority claimed from JP63118118A external-priority patent/JPH01290797A/ja
Priority claimed from JP63118119A external-priority patent/JPH01290798A/ja
Priority claimed from JP13831988A external-priority patent/JPH01309998A/ja
Priority claimed from JP63191521A external-priority patent/JPH0243398A/ja
Priority claimed from JP23226688A external-priority patent/JPH0280598A/ja
Priority claimed from JP23226588A external-priority patent/JPH0280597A/ja
Application filed by Nippon Steel Corp filed Critical Nippon Steel Corp
Publication of EP0342585A1 publication Critical patent/EP0342585A1/de
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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
    • C25D15/00—Electrolytic or electrophoretic production of coatings containing embedded materials, e.g. particles, whiskers, wires
    • C25D15/02—Combined electrolytic and electrophoretic processes with charged materials
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
    • C25D11/38—Chromatising
    • 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
    • C25D3/565—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of zinc
    • 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
    • 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
    • C25D5/60—Electroplating characterised by the structure or texture of the layers
    • C25D5/605—Surface topography of the layers, e.g. rough, dendritic or nodular layers
    • C25D5/611—Smooth layers
    • 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
    • C25D5/627—Electroplating characterised by the visual appearance of the layers, e.g. colour, brightness or mat appearance

Definitions

  • the present invention relates to coated steel sheets or strips (herein called steel sheets) having a coating which can provide excellent corrosion resistance, particularly corrosion resistance in their worked portions, and useful for applications in automobiles home electric appliances, and constructions
  • Galvanized steel sheets have long been used widely as a surface treated steel sheet because they can be commercially produced on a mass-production scale without sacrificing their corrosion resistance before or after paint coating and workability as well as strength inherent to cold rolled steel sheets.
  • alloy coatings As the means for meeting with the demand for improved corrosion resistance of the galvanized steel sheets, it has been known and commonly practiced to increase the amount of the zinc coating itself and in addition to the increased zinc coating amount, various proposals have been made for alloy coatings as a means of inhibiting the dissolution of the zinc coating itself. Most of these proposed alloy coatings contain iron-group metals such as Fe, Ni and Co as the alloying element.
  • the steel sheets electro-plated with a zinc-iron-group-metal coating as disclosed in JP-B- 50-29821 and 57-61831, for example, are characterized by their excellent corrosion resistance before and after paint coating and have been successful in commercial production and application. However, a strong demand still exists for further improvement of their corrosion resistance.
  • a complex coated steel sheet has been developed by subjecting the metallic primer coating to a chromating treatment and then applying an organic coating thereon.
  • the corrosion resistance of the steel sheets having a metallic-organic complex coating mentioned above is imparted mainly by the organic coating.
  • the thickness of the organic coatings is required to be thinner from the points of press formability and weldability, improvement of the metallic primer coating itself is required from the point of corrosion resistance.
  • the organic coating is further thinned when subjected to the press forming and slight damage or scratches can easily penetrate the thinned organic coating to reach the metallic primer coating or even to the substrate steel sheet, thus causing local exposure of the metallic coating of the substrate sheet. Therefore, the corrosion resistance of these coated sheets must more and more rely on the corrosion resistance of the metallic primer coating alone.
  • the conventional metallic coatings cannot impart satisfactory corrosion resistance, and is not reliable for maintaining good corrosion resistance after press forming.
  • the present invention is based on the discovery that it is possible to achieve a markedly enhanced chromium content in the alloy coating, which has never been conventionally achieved, if a water soluble cationic polymer is added to a plating bath containing Zn2+ and Cr3+ which promotes the precipitation of Cr, and that the resultant coating has satisfactory workability due to the co-precipitation of a very small amount of the cation polymer in the coating.
  • the present invention is based on the discovery that addition of iron-group metal or metals, Fe, Ni and Co, to the coating will improve the spot weldability as required for the applications in automobiles and home electric appliances.
  • the present invention is based on the discovery made by further studies by the present inventors that chromium when present with zinc will not be passivated, but tends to take part in a sacrificial rust prevention together with zinc, and the corrosion product of chromium accumulates and forms a hard-to-dissolve protective film, thereby preventing a further progress of corrosion. This phenomenon is considered to provide a high degree of corrosion resistance.
  • the hard-to-dissolve protective film formed by the corrosion product of chromium is very likely to be cracked due to a long time of drying. Therefore, after the lapse of a certain period of time, corrosion can sharply progress. It is found by the present inventors that it is effective to co-precipitate fine particles of oxides in the coating for preventing such sharp development of corrosion.
  • the fine particles of oxides intrude into the corrosion products of zinc and chromium to be strongly combined therewith.
  • the corrosion products thus combined with the oxides can still provide good humidity absorbing ability so that the protective film formed with the corrosion products is hardly strained even under the dry condition, resulting in effective prevention of cracking occurring in the protective film.
  • a further object of the present invention is to provide a coated steel sheet having a primer Zn-Cr coating, an intermediate chromate film, and an upper-most organic coating, which shows excellent corrosion resistance particularly at worked portions, and excellent workability and weldability as well.
  • the Zn-Cr coating contains fine particles of oxide co-precipitated therewith so as to produce corrosion products which are very effective to protect the substrate sheet in event corrosion should occur locally at paint-coating-defective portions or worked portions.
  • a still further object of the present invention is to provide a process for consistently producing the coated steel sheets having a high-chromium alloy coating excellent in corrosion resistance and surface brightness.
  • a water soluble cation polymer is introduced into the Zn-Cr electro-plating bath to promote the precipitation of chromium, and the ratio of Cr6+ ions to Cr3+ ions in the bath is maintained below a certain constant value by the anodic oxidation of Cr3+.
  • the excellent corrosion resistance of the electro-plated steel sheets according to the present invention is imparted mainly by the chromium content in the primer coating.
  • the chromium content in the primer coating For this purpose, 5 to 30 % by weight of Cr in the coating is desirable. With the Cr content less than 5 % by weight in the coating, the tendency of red rust formation is still present and the resultant corrosion resistance is not sufficient, although some improvement is obtained. While with the Cr content not less than 5 %, the red rust formation during a salt spray test, for example, can be inhibited and marked improvement can be obtained.
  • the high degree of corrosion resistance imparted by the coated steel sheets according to the present invention have never been achieved by the conventional Zn coating, or Zn-alloy coatings, such as Zn-Fe and Zn-Ni coatings.
  • the cation polymer used in the present invention is discovered to be effective to promote the precipitation of Cr during the electro plating and also co-precipitates with Cr in the coating in a very small amount, thus improving the anti-powdering property.
  • This advantageous effect by the co-precipitation of the cation polymer is assumed to derive from the fact that the co-precipitation prevents the Cr ions from hindering a uniform electro-deposition and growth of Zn and iron-group metals so that a uniform and smoothly coated structure is assured.
  • the co-precipitation of the cation polymer in the coating it is possible to obtain a dense coating in which Zn and Cr or Zn, Cr and the iron-group metals are uniformly mixed or alloyed.
  • 0.005 to 5 % by weight of cation polymer contained in the coating is desirable. Less than 0.005 %, no tangible effect is obtained for improving the anti-powdering property. On the other hand, the cation polymer content more 5 % in the coating is difficult to obtain even if the cation polymer concentration in the plating bath is increased, and an excessive cation polymer content in the coating tends to lower the coating adhesion. From the point of working alone, it is enough if the cation polymer is co-precipitated in the coating in an amount not less than 1/1000 of the Cr content in the coating.
  • polymers of quaternary amine having a molecular weight from 103 to 106 are preferred.
  • polyaminesulfon (hereinafter called PAS) and polyamine (hereinafter called PA) are most effective to promote the precipitation of Cr. This is attributable to the adsorption effect by the amine group and the combination of the sulfo group with the metal ions or with the metal.
  • the cationic polymer used in the present invention is a homopolymer or copolymer having in its main chain a salt of quaternary amine (ammonium salt) shown below.
  • R1, R2, R3 and R4 are each an alkyl group having 1 to 4 carbon atoms.
  • polymers of primary, secondary and tertiary amines may also be used for promoting the precipitation of Cr although they are less effective.
  • 10 to 50 g/m2 is enough for assuring the desired corrosion resistance, and unavoidable impurities such as Pb, Sn, Ag, In, Bi, Cu, Sb, As, Al, Ti, Na, P and S may be present in a minor amount in the primer coating without degrading the desired properties of the present coated products.
  • the ion-group metal such as Fe, Ni and Co
  • the primer coating in an amount of 1 to 10 % by weight.
  • the Zn-Cr electro-plated coating containing no iron-group metal show inferior spot weldability as compared with the conventional Zn-Ni and Zn-Fe alloy coatings.
  • the reason for the inferior spot weldability may be attributed to the following facts that as compared with the conventional Zn-Ni and Zn-Fe coatings the Zn-Cr coating containing no iron-group metal has a lower electric resistance and is more easily heated and fused by the current passage and further the coating itself is softer and is easily deformed by the pressure exerted thereon by a welding tip so that the current can hardly be concentrated on the welding spot.
  • the Zn-Cr coating contains the iron-group metal, such as Fe, Ni and Co
  • the electric resistance is enhanced and the coating itself is hardened so that the spot weldability is definitely improved.
  • the iron-group metal content in an amount less than 1 % by weight is not effective for the purpose, while in excess of 10 % by weight, the coating is influenced largely by the nature of the iron-group metal so that corrosion resistance is, in some cases, deteriorated.
  • the iron-group metal When the iron-group metal is present in the electro-plating bath, it produces favorable effect that the ions of this metal adsorbs on the fine particles of oxide, if present, to facilitate the precipitation of the oxide.
  • the total amount of the iron-group metal in the coating is excessively increased, the workability of the coating is deteriorated despite the favorable effect of the co-precipitation of the cation polymer. Therefore, it is desirable to maintain the total content of Cr and the iron-group metal in the coating not more than 30 % by weight.
  • the iron-group metal Ni is most desirable because it can further improve the corrosion resistance of the coating.
  • the fine particles of oxide contained in the coating contribute to further stabilize the corrosion products of Zn-Cr by intrusion thereinto and strong combination therewith through oxygen bonding, and the fine particles of oxide act as a barrier against corrosive factors. In this way the corrosion resistance of the coated steel sheet, particularly the corrosion resistance at and around the worked portions, is improved.
  • the fine particles of oxide are contained in the coating in an amount from 0.1 to 10 % by weight. Less than 0.1 %, no substantial improvement of corrosion resistance is obtained and more than 10 %, workability is deteriorated. From aspects of both corrosion resistance and workability, 0.1 to 5 % by weight of the fine particles of oxide is more preferable.
  • oxides As the fine particles of oxide usable in the present invention, many metal oxides and semi-metal oxides may be used, but oxides of Si, Al, Zr, Cr, Mo and W are most preferable. These oxides can be used in single or in combination.
  • the particle size of these oxides is preferably not larger than 1 ⁇ m in average. The particle size larger than 1 ⁇ m is hard to co-precipitate in the coating.
  • the primer coating according to the present invention may be of homogeneous or heterogeneous structure.
  • one or more specific components may be dispersed or condensed in a layer form, or the concentration of specific component or components may vary in gradient across the coating thickness.
  • coated steel sheets having the primer coating described hereinabove may further be coated with a Zn or Zn-alloy coating such as Zn-Fe and Zn-Ni coatings in a small amount.
  • the primer coating may be subjected to a chromate treatment and then further coated with an organic coating.
  • the chromate film applied on the primer coating is effective to enhance the adhesion with the organic coating.
  • any of the conventional chromate treatments such as the spray type chromate treatment, the reaction type chromate treatment, and the electrolytic type chromate treatment may be applied.
  • inorganic colloids such as phosphoric acid, fluoride, water-soluble or emulsion type organic resin may be added to the treating solution in addition to Cr6+ and Cr3+ as conventionally done.
  • the solution containing the phosphoric acid and the fluoride may be composed of 30 g/l of chromic acid, 10 g/l of phosphoric acid, 4 g/l of potassium titanate fluoride, and 0.5 g/l sodium fluoride.
  • the treating solution containing the silica the solution may be composed of 50 g/l of chromic acid (including 40 % of trivalent chromium) and 100 g/l of SiO2.
  • colloids of SiO2, Al2O3, TiO2 and ZrO2 colloids containing one or more of oxyacids such as molybdic acid, tungstic acid, vanadic acid, and their salts; phosphoric acids such as phosphoric acid and polyphosphoric acid which form hard-to-dissolve salts by reaction with Zn of the coating; and silicofluorides titanium, and phosphates which form hard-to-dissolve salts by reaction such as hydrolysis.
  • colloids are found to be effective to fix a small amount of hexavalent chromium in the chromate film and also phosphoric acids and fluorides mentioned above in particular are found to be effective to promote the reaction between the primer coating and the chromate.
  • the amount of these inorganic colloids to be added may vary depending on their natures; in the case of phosphoric acids, 1 to 200 g/l is desirable, and in the case of SiO2, 1 to 800 g/l is desirable, for example.
  • organic resins such as acrylic resin, which are consistently mixable with the chromate may be added.
  • any conventional treatment can be applied, such as one in which sulfuric acid, phosphoric acid, and halogen ions are added in addition of chromic acid, or inorganic colloids such as SiO2 and Al2O3 are added, or cations such as Co and Mg are added.
  • the electrolysis is performed by the cathodic electrolysis, but the anodic electrolysis and alternate current electrolysis may be additionally used.
  • the amount of chromate film formed on the primer coating is preferably from 10 to 150 mg/m2 in the term of total chromium. With a chromate film of less than 10 mg/m2, the adhesion of the organic film is not satisfactory, while a chromate film of more than 150 mg/m2, the weldability and press formability deteriorate. Therefore, from the practical point, 20 to 100 mg/m2 is more desirable.
  • an organic coating of 0.3 to 3 ⁇ m in thick may be applied for improving the corrosion resistance.
  • an organic coating less than 0.3 ⁇ m the desired improvement of corrosion resistance cannot be assured, and with an organic coating exceeding 3 ⁇ m, weldability and press formability may sometimes deteriorate.
  • a more preferable range is from 0.5 to 2 ⁇ m.
  • the organic coating may be either a solvent type or a water soluble type, and epoxy and acrylic resins, polyester, urethane and acrylic olefins etc., and their copolymer derivatives may be used, for example.
  • the organic coating may be applied by any conventional methods, such as roll coating, spray coating, and curtain flow coating.
  • the coated steel sheet may be coated only one side, and the other side may be uncoated or coated with the Zn-Cr coating alone depending on the final applications the coated steel sheet is intended for.
  • the electo-plating may be performed in a plating bath containing Zn2+ ions, Cr3+ ions, and 0.01 to 20 g/l of water soluble cation polymer, such as copolymers of tertiary amines as mentioned hereinbefore, having a pH value ranging from 0.5 to 3 at a bath temperature ranging from 40 to 70°C with a current density of 20 A/dm2 or higher.
  • a plating bath containing Zn2+ ions, Cr3+ ions, and 0.01 to 20 g/l of water soluble cation polymer, such as copolymers of tertiary amines as mentioned hereinbefore, having a pH value ranging from 0.5 to 3 at a bath temperature ranging from 40 to 70°C with a current density of 20 A/dm2 or higher.
  • the iron-group metals, and fine particle oxides, such as SiO2, TiO2 and Al2O3 are added to the bath. Further the addition of salts of Na+, K+, and NH4+ ions are advantageous for improving the electric conductivity of the bath.
  • the Zn coating or Zn-alloy coating to be formed on the primer coating may be done by a conventional plating method. In this case, however, it is most desirable to completely remove the dragout containing Cr ions and cation polymer taken out from the primer coating bath with water prior to the coating.
  • a dull-finished rolled soft steel sheet is normally used.
  • a bright-finished rolled steel sheet may be used, and the steel composition may be a high tensile steel containing larger amounts of Mn, S and P or may be a corrosion resistant steel containing larger amounts of Cr, Cu, Ni and P.
  • Fig. 1 is a drawing showing the shape of welding tip used for evaluating the spot-weldability.
  • Fig. 2 is to show the correlation between the surface brightness and the Cr content and the ratio of Cr6+/Cr3+ and in a typical plating bath used in the present invention, showing that the ratio of Cr6+/Cr3+ not more than 0.1 is essential.
  • a cold rolled steel sheet with a thickness of 0.8 mm was subjected to alkali degreasing, acid pickling with the use of 5 % sulfuric acid solution and washing in succession, and then the resultant steel sheet was electro-plated in an acidic bath of sulfuric acid at pH 2 at a bath temperature of 60°C, with a flow rate of the solution of 90 m/min by pump stirring, and the distance between the electrodes of 10 mm.
  • the plating bath was composed of 70 g/l of Zn2+ ion, 1 - 30 g/l of Cr3+ ion, 0.01 - 20 g/l of cationic polymer (polyamine polymer (PA) with molecular weight of 10,000 or polyamine-sulfone polymer (PAS) with molecular weight of 120,000) and 16 g/l of Na+.
  • the contents of Cr and cationic polymer were controlled by their addition amounts and the electric current density.
  • the plated amount was 20 g/m2.
  • Zn or Zn-alloy coating was applied in an amount of 3 g/m2 as a topcoat by means of a known method.
  • the coating compositions and evaluation of corrosion resistance and workability of the electro-plated steel sheets produced in this way are shown in Table 1.
  • Zn and Cr in the coating were analysed by means of the atomic absorption method and, as for the cationic polymer, C was analyzed by the combustion method and the amount of cationic polymer was recalculated therefrom.
  • the methods for the evaluation of corrosion resistance and workability are as follows:
  • the Zn-Cr coated samples were subjected successively to immersion type phosphoric acid treatment, cathodic electric coating of Zn with a thickness of 20 ⁇ m, intermediate coating, water polishing and topcoat paint coating to obtain a total thickness of coatings of 100 ⁇ m.
  • the test pieces were given a crosscut reaching to the base metal and subjected to the 1,000 hour SST and the 60 cycle CCT as above mentioned, and the results were evaluated by means of the swollen width of the crosscut part. less than 1 mm: o 1 mm - 3 mm: ⁇ 3 mm - 5 mm: ⁇ more than 5 mm: ⁇
  • the coating compositions and evaluation of corrosion resistance, spot weldability and workability of the electro-plated steel sheets produced in this way are shown in Table 2.
  • Zn, Cr, Fe, Co and Ni in the coating were analyzed by means of the atomic absorption method and, for the cationic polymer, the amount of carbon was analyzed by the combustion method and the amount of cationic polymer was recalculated therefrom.
  • the methods for evaluating corrosion resistance and workability were the same as in Example 1. Spot weldability was evaluated by the following method.
  • the welding conditions were as below.
  • the plated steel sheet in the above was subjected to cathodic electrolysis with a current density of 10 A/dm2 at a bath temperature of 40°C, and the resultant product was washed and dried.
  • the amount of chromate to be formed was controlled by means of the amount of coulomb.
  • the coated steel sheets were immersed in a treating solution comprising 50 g/l of chromic acid (containing Cr3+ 40 %), 100 g/l of colloidal SiO2 at a bath temperature of 40°C.
  • the resultant coated steel sheets were dried for 1 min at 100°C after air-wipe treatment.
  • the amount of chromate to be formed was controlled by means of the dilution ratio of the treating solution and the pressure at the air-wipe treatment.
  • a treating solution containing 50 g/l of chromic acid, 10 g/l of phosphoric acid, 0.5 g/l of NaF and 4 g/l of K2TiF6 was sprayed on coated steel sheets at a bath temperature of 60°C, and the resultant coated steel sheets were dried at 60°C after washing.
  • the amount of chromate was controlled by means of the dilution ratio of the treating solution and the duration of its spraying.
  • coated steel sheets obtained by the above mentioned chromate treatment were further subjected to organic coating under the following conditions.
  • the salt spray test JIS Z2371 was done for 2,000 hours, and the evaluation was done with respect to the red-rust-suffering area in the worked portions. less than 1 %: o 1 % - 5 %: ⁇ 5 % - 10 %: ⁇ more than 10 %: ⁇
  • plating was done under the same conditions as in Example 1.
  • compositions of primer coatings and results of evaluation are as shown in table 4.
  • the methods for determining metal constituents as well as the cationic polymers used are same as in Examples 1 and 2.
  • the methods for evaluating corrosion resistance and workability are as below.
  • Salt spray test (exposed at Chiba district by spraying 5 % saline water once a week) was done, and the results were evaluated by the area where red rust formed after one year exposure. less than 1 %: o 1 % - 10 %: ⁇ 10 % - 30 %: ⁇ more than 30 %: ⁇
  • Example 2 The welding was done under the conditions as shown in Example 2, and the results were evaluated according to the following method, i.e., to measure the diameter of nugget after continuous shock of 3,000 times. more than 4 mm: o 3 mm - 4 mm: ⁇ less than 3 mm: ⁇
  • Example 4 Plating was done under the same conditions as in Example 4, and the resultant coated steel sheets were subjected to chromate treatment and organic film coating treatment in succession under the same conditions as in Example 3.
  • the salt spray test JIS Z2371 was done for 3,000 hours, and the evaluation was done with respect to the red-rust-suffering area at the worked portions. less than 1 %: o 1 % - 5 %: ⁇ 5 % - 10 %: ⁇ more than 10 %: ⁇
  • Corrosion resistance was evaluated by the area of red rust after 500 hours salt spray test (JIS Z2371). less than 1 %: o 1 % - 10 %: ⁇ 10 - 30 %: ⁇ more than 30 %: ⁇ Surface brightness was evaluated by brightness degree (JIS Z8741, G s (60°), standard value of black glass plate: 93).
  • coated products obtained by the examples of the present invention those with the Cr content of not less than 5 wt.% are particularly excellent in corrosion resistance. All of the examples were excellent in the surface brightness.
  • No. 6-27 and 6-29 do not contain cationic polymer in the plating bath and thereby the current density is not sufficiently high, so that the Cr content in the coating is only in a trace amount and the corrosion resistance is not good.
  • No. 6-28 and 6-30 do not contain cationic polymer, since the current density is sufficiently high to increase, the Cr content and the corrosion resistance is excellent, but their surface appearance is inferior.
  • No. 6-31 and 6-32 since the ratio of Cr6+/Cr3+ in the plating bath is high, the Cr content in the primer coating is low, corrosion resistance is insufficient and surface appearance, too, is inferior.
  • the efficiency of all the comparison examples is as low as 50 % or lower.
  • the plating solution was circulated through a bath filled with Zn metal, and then the Cr6+/Cr3+ ratio was decreased. After the Cr6+/Cr3+ ratio was lowered to 0.1, the plating was done again under the above mentioned condition, and the coating with the Cr content of 7 wt.% and having excellent surface brightness could be obtained.
  • Continuous electro-plating was done thereafter by passing the plating solution occasionally through the tank filled with metallic Zn and repeating the measurement of the Cr6+/Cr3+ ratio in the bath periodically.
  • a coating with the Cr content of not less than 6 wt.% and excellent surface brightness could be obtained under the condition that the Cr6+/Cr3+ ratio in the bath was not more than 0.1.
  • Example 7 With an anode of Pb-5% Sn and using a plating bath same as in Example No. 6-7, electro-plating was done under the condition of Example 7. The result was the same as in Example 7 until the Cr6+/Cr3+ ratio did not exceed 0.1.
  • Fe2+ ion in an amount of 5 g/l to the bath at the time when the Cr6+/Cr3+ ratio reached to 0.5, the Cr6+/Cr3+ ratio lowered to 0.05, and a coating with the Cr content of 10 wt.% and having excellent surface brightness could be obtained.
  • the present invention it is possible according to the present invention to produce a composite electro-plated steel sheet having a primer coating comprising Zn as main constituent, containing simultaneously a large quantity of Cr and having excellent surface brightness which has been very difficult to produce by the conventional arts.
  • the coated products according to the present invention are very suitable for the production of a rust preventing steel sheet for such uses as in automobiles, home electric appliances and constructions in which high corrosion resistance and excellent surface brightness are required.

Claims (12)

  1. Beschichtetes Stahlblech mit einer Grundierungsbeschichtung, die 5 bis 30 Gew.-% Cr und 0.005 bis 5 Gew.-% eines kationischen Polymers aufweist und gegebenenfalls mindestens 1 Gew.-% eines Metalls der Eisengruppe und/oder 0.1 bis 10 Gew.-% feiner Oxidteilchen aufweist, wobei der Rest Zn ist.
  2. Beschichtetes Stahlblech gemäß Anspruch 1, wobei die Gesamtmenge von Cr und dem Metall der Eisengruppe höchstens 30 Gew.-% beträgt.
  3. Beschichtetes Stahlblech gemäß Anspruch 1 oder 2, wobei die Grundierungsbeschichtung 1 bis 10 Gew.-% eines Metalls der Eisengruppe aufweist.
  4. Beschichtetes Stahlblech gemäß einem der Ansprüche 1 bis 3, wobei der Gehalt des Metalls der Eisengruppe in einem Bereich von 1/10 bis 1/2 des Cr-Gehalts liegt.
  5. Beschichtetes Stahlblech gemäß einem der Ansprüche 1 bis 4, wobei das Oxid aus der Gruppe, die aus den Oxiden von Si, Al, Zr, Ti, Cr, Mo und W besteht, ausgewählt wird.
  6. Beschichtetes Stahlblech gemäß einem der Ansprüche 1 bis 5, wobei das kationische Polymer ein quarternäres Aminpolymer ist.
  7. Beschichtetes Stahlblech gemäß einem der Ansprüche 1 bis 6, welches ferner eine auf der Grundierungsbeschichtung ausgebildete Beschichtung aus Zn oder einer Zn-Legierung umfaßt.
  8. Beschichtetes Stahlblech gemäß einem der Ansprüche 1 bis 6, welches ferner einen Chromatfilm, der auf der Grundierungsbeschichtung mit einer gesamten Chrommenge von 10 bis 150 mg/m² ausgebildet ist, und eine organische Beschichtung umfaßt, die mit einer Dicke von 0.3 bis 3 µm auf dem Chromatfilm ausgebildet ist.
  9. Verfahren zur Herstellung eines beschichteten Stahlblechs mit einer Grundierungsbeschichtung, die 5 bis 30 Gew.-% Cr und 0.005 bis 5 Gew.-% eines kationischen Polymers aufweist, und mit ausgezeichneter Korrosionsbeständigkeit und ausgezeichnetem Oberflächenglanz, wobei das Verfahren die Durchführung einer Elektroplattierung in einem säurehaltigen galvanischen Zn-Bad umfaßt, das Cr-Ionen und ein kationisches Polymer enthält, wobei das Verhältnis von Cr⁶⁺-Ionen/Cr³⁺-Ionen höchstens 0.1 beträgt.
  10. Verfahren gemäß Anspruch 9, bei dem das säurehaltige Bad Ni²⁺, Fe²⁺ und/oder Co²⁺ enthält.
  11. Verfahren gemäß einem der Ansprüche 9 und 10, bei dem das säurehaltige Bad ferner mindestens ein Oxid von Si, Al, Zr, Ti, Cr, Mo und W enthält.
  12. Verfahren gemäß einem der Ansprüche 9 bis 11, bei dem das kationische Polymer ein quarternäres Aminpolymer ist.
EP89108750A 1988-05-17 1989-05-16 Beschichtete Stahlbleche und Verfahren zu deren Herstellung Expired - Lifetime EP0342585B1 (de)

Applications Claiming Priority (12)

Application Number Priority Date Filing Date Title
JP63118118A JPH01290797A (ja) 1988-05-17 1988-05-17 耐食性に優れた複合電気めっき鋼板
JP118118/88 1988-05-17
JP118119/88 1988-05-17
JP63118119A JPH01290798A (ja) 1988-05-17 1988-05-17 耐食性と溶接性に優れた複合電気めっき鋼板
JP138319/88 1988-06-07
JP13831988A JPH01309998A (ja) 1988-06-07 1988-06-07 耐食性と表面光沢に優れた複合電気めっき鋼板の製造方法
JP63191521A JPH0243398A (ja) 1988-07-29 1988-07-29 耐食性に優れた有機複合めっき鋼板
JP191521/88 1988-07-29
JP23226688A JPH0280598A (ja) 1988-09-19 1988-09-19 耐食性に優れた有機複合めっき鋼板
JP23226588A JPH0280597A (ja) 1988-09-19 1988-09-19 高耐食性複合電気めっき鋼板
JP232266/88 1988-09-19
JP232265/88 1988-09-19

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EP0342585A1 EP0342585A1 (de) 1989-11-23
EP0342585B1 true EP0342585B1 (de) 1993-08-18

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5169726A (en) * 1990-08-22 1992-12-08 Kabushiki Kaisha Kobe Seiko Sho Surface treated materials of excellent adhesion for painting layer, corrosion resistance after painting, and press formability, as well as a method of manufacturing them
US5997714A (en) * 1995-10-31 1999-12-07 Kawasaki Steel Corporation Organic coated material having an electrolytically polymerized coating film containing chromium and method
GB2340131A (en) * 1998-07-29 2000-02-16 Ford Motor Co Corrosion resistant surface coating based on zinc

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CA993831A (en) * 1971-07-07 1976-07-27 Iwakichi Kawaguchi Chromate treated metal sheet and a process therefor
ES8607426A1 (es) * 1984-11-28 1986-06-16 Kawasaki Steel Co Mejoras y procedimiento para la fabricacion de flejes de acero plaqueados compuestos con alta resistencia a la corro-sion

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EP0342585A1 (de) 1989-11-23
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DE68908471D1 (de) 1993-09-23

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