SURFACE-TREATED STEEL SHEET EXCELLENT IN CORROSION RESISTANCE AFTER WORKING

摘要

Object: to develop a material which can be improved in the resistance to corrosion caused by alcoholic fuels after working without detriment to the weldability and without any substantial cost increase. Constitution: a chromate coating is formed on Zn-X-alloy electroplated steel sheets (wherein X is at least one element selected among 3-18 wt.% Ni, 0.02-3 wt.% Co, 25-45 wt.% Mn, and 8-20 wt.% Cr). The crack density of the Zn-X-alloy coating present under the chromate coating is 1,000-150,000/mm2 in terms of the spot surrounded by the cracks, among which cracks having the maximum width of 0.5 µm or less account for at least 90 % and cracks whose depths are at least 80 % of the coating thickness account for at least 80 %.