FIELD: chemistry.
SUBSTANCE: solution for chemical treatment of the steel sheet with a plating coating based on zinc contains soluble molybdate, vanadium salt, amine, oxoat of element 4 of the Periodic Table of Chemical Elements group, and a phosphate compound. The molar ratio of molybdenum to vanadium in the solution for the chemical treatment is from 0.4 to 5.5, the mole ratio of amine to vanadium in the solution for the chemical treatment is 0.3 or more, the content of the hydrophilic resin in the solution for the chemical treatment is not more than 100 wt % per the total amount of vanadium and molybdenum in the solution for the chemical treatment. The total content of fluoride due to fluoride ion or metalloprotein ion in the solution for the chemical treatment is not more than 30 wt % per the total amount of vanadium and molybdenum in the solution for the chemical treatment, and the silicon content due to the silanole group, in the solution for the chemical treatment is not more than 50 wt % per the total amount of vanadium and molybdenum in the solution for the chemical treatment. The said steel sheet has a zinc-based cladding layer containing from 0.1 to 22.0 wt % of aluminium and a chemical conversion film disposed thereon. The chemical conversion film includes the first chemical conversion layer placed on the surface of the cladding coating based on zinc and containing vanadium, molybdenum, and phosphor, and the second chemical conversion layer placed on the first chemical conversion layer containing the element oxoat of Group 4 of the Periodic Table of Chemical Elements. The percentage of pentavalent vanadium based on vanadium of mixed valence in the chemical conversion film is 0.7 or more.
EFFECT: production of a steel sheet with improved corrosion resistance and blackening resistance.
5 cl, 3 dwg, 41 tbl, 4 ex
