Chemical conversion treatment solution and chemically converted steel sheet

Abstract

A chemically converted steel sheet having a chemically converted coating film is made by coating a Zn-based plated steel sheet with a chemical conversion treatment solution and drying the same. The chemically converted coating film is constituted by a first chemically converted layer including V, Mo, and P, and a second chemically converted layer provided on said layer and including a group 4A metal oxygen acid salt, and the ratio of pentavalent V to all the Vs in the chemically converted coating film is 0.7 or greater. The chemical conversion treatment solution includes specific proportions of V, Mo, an amine, the group 4A metal oxygen acid salt, and P, and substantially does not include hydrophilic resins, fluorine, or silicon.

1 . A chemical treatment solution for coating a zinc-based plated steel sheet having a zinc-based plating layer containing 0.1 to 22.0 mass % of aluminum, the chemical treatment solution comprising:
 a water-soluble molybdate;   a vanadium salt;   an amine;   a group 4A metal oxoate; and   a phosphate compound,   wherein:   a molar ratio of molybdenum to vanadium in the chemical treatment solution is 0.4 to 5.5,   a molar ratio of the amine to the vanadium in the chemical treatment solution is 0.3 or more,   a content of a hydrophilic resin in the chemical treatment solution is at most 100 mass % based on a total amount of the vanadium and the molybdenum in the chemical treatment solution,   a total content of fluorine derived from a fluorine ion or a fluorometal ion in the chemical treatment solution is at most 30 mass % based on the total amount of the vanadium and the molybdenum in the chemical treatment solution, and   a content of silicon derived from a silanol group in the chemical treatment solution is at most 50 mass % based on the total amount of the vanadium and the molybdenum in the chemical treatment solution.   
     
     
         2 . The chemical treatment solution according to  claim 1 , wherein the amine has a molecular weight of 80 or less. 
     
     
         3 . A chemically treated steel sheet comprising:
 a zinc-based plated steel sheet having a zinc-based plating layer containing 0.1 to 22.0 mass % of aluminum, and a chemical conversion film disposed on the zinc-based plating layer,   wherein:   the chemical conversion film includes a first chemical conversion layer disposed on a surface of the zinc-based plating layer and containing vanadium, molybdenum and phosphorus, and a second chemical conversion layer disposed on the first chemical conversion layer and containing a group 4A metal oxoate, and   a percentage of pentavalent vanadium based on mixed-valent vanadium in the chemical conversion film is 0.7 or more.   
     
     
         4 . The chemically treated steel sheet according to  claim 3 , wherein:
 the group 4A metal oxoate is a zirconium oxoate, and   the chemical conversion film contains 1 to 60 parts by mass of molybdenum, 2 to 20 parts by mass of vanadium, and 10 to 50 parts by mass of phosphorus, based on 100 parts by mass of zirconium.   
     
     
         5 . The chemically treated steel sheet according to  claim 3 , wherein the zinc-based plated steel sheet is a hot-dip aluminum- and magnesium-containing zinc plated steel sheet having a hot-dip aluminum- and magnesium-containing zinc plating layer containing 0.1 to 22.0 mass % of aluminum and 1.5 to 10.0 mass % of magnesium. 
     
     
         6 . The chemically treated steel sheet according to  claim 4 , wherein the zinc-based plated steel sheet is a hot-dip aluminum- and magnesium-containing zinc plated steel sheet having a hot-dip aluminum- and magnesium-containing zinc plating layer containing 0.1 to 22.0 mass % of aluminum and 1.5 to 10.0 mass % of magnesium.