| 摘要 |
PROBLEM TO BE SOLVED: To obtain a chemically treated steel sheet having excellent seam weldability, coating material adhesion and corrosion resistance by executing cathode electrolysis in a low temp. bath whose compsn. and temp. are specified and thereafter executing immersing treatment in a temp. bath contg. CrO3 and having a specified temp. SOLUTION: A nickel plated steel sheet is subjected to cathode electrolytic treatment in a treating bath of <45 deg.C bath temp. at least contg. CrO3 and H2SO4 of 1/50 to 1/300 by the weight ratio with CrO3 and is successively subjected to immersing treatment in a treating bath of >=50 deg.C at least contg. CrO3. The the reduction of the temp. of the electrolytic treating bath, the uniform covering ability of metallic chromium improves. Furthermore, hydrated chromium oxide has a double layer structure of an ol type compd. in the upper layer and an oxo type compd. in the lower layer, though, by the reduction of the temp. of the electrolytic treating bath, the amounts of both compds. to be precipitated increase, the amt. of sulfuric acid ions to be precipitated into the ol type compd. increases, and the meltability of the ol type compd. in the following immersing treatment increases. As a result, the ol type compd. reduces, and the purpose can be attained.
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