PRODUCTION OF CHROMATE TREATED LEAD-CONTAINING GALVANIZED STEEL SHEET EXCELLENT IN BLACKENING RESISTANCE AND WHITE RUST RESISTANCE

摘要

PROBLEM TO BE SOLVED: To stably produce a lead-contg. galvanized steel sheet excellent in appearance, blackening resistance and white rust resistance by applying a specified chromate treating soln. to a specified galvanized steel sheet and drying the same at a specified temp. ;SOLUTION: A lead-contg. galvanized steel sheet is formed by a galvanizing bath, e.g. contg., by weight, 0.05 to 0.3% Pb and 0.1 to 0.3% Al. It is subjected to washing and drying, is coated with a chromate treating soln. and is dried at 40 to 250°C without washing to form chromium coating with 5 to 250mg/cm² coating weight expressed in terms of metallic chromium. The chromate treating soln. to be applied is the one contg. sexivalent chromium ions, trivalent chromium ions and nitric acid ions, in which the molar ratio of the trivalent chromium ions/the sexivalent chromium ions is regulated to 1/9 to 1/1, and the molar ratio of the nitric acid ions to the total chromium ions is regulated to 0.1 to 1.6. In this way, the blackening resistance and white rust resistance of the lead-contg. galvanized steel sheet can be improved without executing flash treatment by Ni, Co or the like.;COPYRIGHT: (C)1998,JPO