SURFACE TREATED STEEL PLATE FOR FUEL TANKS

摘要

A surface-treated steel sheet for fuel tanks comprising a Zn-X alloy plating layer + a chromate film, in which the Zn-X alloy plating layer has an X content for the plating metal as a whole of Ni: 9 - 18 wt%, Co: 0.02 - 3 wt%, Mn: 25 - 45 wt%, or Cr: 8 - 20 wt%, the amount of deposition of the plating layer is 5 - 40 g/m<2> and the amount of the chromate film is 10 - 200 mg/m<2> on a metallic Cr basis, the Zn-Ni alloy plating layer corresponding to at least the inner surface of a tank has: (1) cracks in the surface layer, with the density of the cracks being 1000 - 150000 in terms of the number of plated regions surrounded by cracks in a visual field of 1 mm x 1 mm, and the maximum width of the cracks is not more than 0.5 mu m, or (2) an X/(X+Zn) atomic percentage (X2) determined by surface analysis based on ESCA with X1 NOTEQUAL X2 (wherein X1 = average value of the x content of the plating metal as a whole), and with X2 being Ni: 5 - 25 at%, Co: 0.009 - 10 at%, Mn: 15 - 65 at% or Cr: 5 - 25 at%.