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Corrosion-resistant surface-coated steel sheet

  • US 5,330,850 A
  • Filed: 12/28/1992
  • Issued: 07/19/1994
  • Est. Priority Date: 04/20/1990
  • Status: Expired due to Fees
First Claim
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1. A surface-coated steel sheet having improved corrosion resistance, comprising a steel sheet having on at least one surface thereof an inorganic-organic composite coating which comprises the following layers (a) to (d) from bottom to top of the coating:

  • (a) a first zinc alloy plating layer with a coating weight of 10-100 g/m2 which contains at least one of nickel (Ni) and cobalt (Co) as an alloying element in an amount satisfying the following inequality;

    
    
    space="preserve" listing-type="equation">0.05≦

    (5×

    Co)+Ni≦

    10 in weight percent,(b) a second zinc alloy plating layer with a coating weight of 0.05-10 g/m2 which contains at least one of Ni and Co as an alloying element in an amount satisfying the following inequality;

    
    
    space="preserve" listing-type="equation">10<

    (5×

    Co)+Ni≦

    40 in weight percent,(c) a chromate film layer with a coating weight of 20-300 mg/m2 as Cr, and(d) an organic coating layer, with a thickness of 0.2-5 μ

    m.

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