| abstract |
PURPOSE:To form a chromate film that is colorless and transparent and has a high degree of corrosion resistance on a plated steel plate by treating said steel plate with a chromating soln. compounded with Cr2O3, Co salt of inorg. acids, silica sol, phosphoric acid and suitable fluoride. CONSTITUTION:A chromating soln. contg. 10-50g/l Cr2O3, 0.4-2.1g/l Co salt of inorg. acids in term of Co (e.g. cobalt nitrate), 0.5-10g/l phosphoric acid and 0.3-4.0g/l F compounds is prepd. The F compd. contains those that dissociate F<+> or flourine complex ions, for which, for example, NH4HF2 or (NH4)2SiF6 is preferable. Next, a plated steel plate (e.g., zinc plated steel plate) of cleaned surfaces is dipped in said treating soln. at 50-70 deg.C, and the excess treating soln. stuck on the steel plate is removed, after which the steel plate is dried without rinsing, whereby the above-mentioned chromate film is formed. |