To provide a galvanized steel sheet in which the individual defects of a manganese based film, a titanium based film and a molybdenum based film are offset each other, and blackening resistance and corrosion resistance after working are remarkably improved.
In this galvanized steel sheet, a chemical conversion film containing soluble compound forming metals such as Mo, V, W, Nb and Ta and composite compounds of Mn, Ti and Co are formed on the surface of a galvanized layer. Mn and Ti as the constituting components of the composite compounds are fed as oxides, fluorides, phosphates, organic acid salts or the like, and the soluble compound forming metals are fed as oxyacid salts. As the organic acid, the one containing a carboxylic group is preferable. The chemical conversion film is formed by coating the galvanized steel sheet with a chemically treating solution containing the oxyacid salts of the soluble compound forming metals, a titanium compound, a molybdic compound, a cobalt compound, phosphoric acid or a phosphate and an organic acid, and whose pH is controlled to 1 to 6 and heating and drying the same at 50 to 200°C without performing water washing.
MORIKAWA SHIGEYASU
MATSUNO MASANORI
NAKANO TADASHI
ARIYOSHI YASUMI
TAKETSU HIROBUMI
