PRODUCTION OF BEAUTIFULLY SPANGLED CHROMATED LEAD-CONTAINING HOT-DIP GALVANIZED STEEL SHEET EXCELLENT IN RESISTANCE TO BLACKENING AND WHITE RUST

摘要

PROBLEM TO BE SOLVED: To obtain the steel sheet without flushing with Ni, etc., by treating a lead-contg. hot-dip galvanized steel sheet produced at specified galvanizing bath temp. and penetration sheet temp. with an aq. alkali soln. at specified pH and then with a chromating soln. contg. nitrate ion and having a specified composition. ;SOLUTION: A lead-contg. hot-dip galvanized steel sheet obtained in a galvanizing bath contg. 0.05-0.3wt.% Pb and 0.1-0.3wt.% Al at 440-500°C bath temp. and 440-520°C penetration sheet temp. is treated with an aq. alkali soln. at pH9 and washed with water. Subsequently, a chromating soln. contg. chromium (VI) ion, chromium (III) ion and nitrate ion and with the molar ratio of chromium (III) ion to chromium (VI) ion controlled to 1/9 to 1/1 and the molar ratio of nitrate ion to total chromium ion to 0.1 to 1.6 is applied and then dried at 40-250°C sheet temp. without being washed with water to form a chromate film at 5-50mg/m² coating weight, expressed in terms of metallic chromium.;COPYRIGHT: (C)1998,JPO