초록 ▼

A chromate film is applied to a Zn--X alloy electroplating layer, in which X is one or more of Ni: 3-18 wt %, Co: 0.02-3 wt %, Mn: 25-45 wt %, or Cr: 8-20 wt %. The Zn--Ni alloy plating layer underlying the chromate film has cracks with a density of 1000-150000 in terms of the number of plated regio

A chromate film is applied to a Zn--X alloy electroplating layer, in which X is one or more of Ni: 3-18 wt %, Co: 0.02-3 wt %, Mn: 25-45 wt %, or Cr: 8-20 wt %. The Zn--Ni alloy plating layer underlying the chromate film has cracks with a density of 1000-150000 in terms of the number of plated regions surrounded by cracks in a 1 mm.times.1 mm visual field, with cracks having a maximum width of 0.5 .mu.m or less comprising 90% or more of the total number of the cracks, and with cracks having a depth of 80% or more of the thickness of the plating layer comprising 80% or more of the total number of the cracks.

대표청구항 ▼

[ What is claimed is:] [1.] A surface-treated steel sheet exhibiting improved corrosion resistance after forming, which comprises a Zn--X alloy electroplated layer in an amount of 5-50 g/m.sup.2 on at least one side of the steel sheet, an alloy composition of the layer being such that X is at least

[ What is claimed is:] [1.] A surface-treated steel sheet exhibiting improved corrosion resistance after forming, which comprises a Zn--X alloy electroplated layer in an amount of 5-50 g/m.sup.2 on at least one side of the steel sheet, an alloy composition of the layer being such that X is at least one substance selected from the group consisting of Ni: 3-18 wt %, Co: 0.02-3 wt %, Mn: 25-45 wt %, and Cr: 8-20 wt %, and a chromate film placed on the Zn--X alloy electroplated layer in an amount of 10-200 mg/m.sup.2 as metallic Cr, the Zn--X alloy plating layer having cracks, the density of which is 1000-150000 in terms of the number of plated regions surrounded by cracks in a visual field measuring 1 mm.times.1 mm, with cracks having a maximum width of 0.5 .mu.m or less comprising 90% or more of the total number of the cracks, and with cracks having a depth of 80 % or more of the thickness of the plating layer comprising 80% or more of the total number of the cracks.