| 摘要 |
PURPOSE:To obtain a titled treated steel plate which causes less degradation of adhesive strength owing to retort treatment by subjecting a steel plate to electrolytic treatment is a soln. contg. fluoride or HF or respectively specified contents of chromic acid and sulfuric acid and weight ratio of F/S. CONSTITUTION:A steel plate is subjected to pretreatment (surface activation) by such a method of dipping the same in a soln. contg. 0.5-20% one or more kinds of organic acids such as formic acid or tartaric acid, after which it is subjected to electrolytic treatment in the following manner. Namely, the steel plate having undergone such pretreatment is subjected to electrolytic treatment in a soln. contg. 40-200g/l chromic acid and <100ppm sulfuric acid groups and contg. alkali metal salt or NH4 salt of F and HF so to make F/S >=10wt%, preferably >=15wt%. NaF, KF, LiF, etc. are used as the alkali metal salt of F. As a result, the amount of SO4 codepositing in hydrated chromium oxide at the electrolysis is made exceedingly small and the steel plate of less degradation in strength of the adhered part is obtained. |
