Surface-treated steel sheet and method for manufacturing the same

A surface-treated steel sheet, comprising:

• a steel sheet;
• and
• a nickel-cobalt-iron diffusion layer formed as an outermost surface layer on the steel sheet,
• wherein when a content of Ni, a content of Co and a content of Fe of the nickel-cobalt-iron diffusion layer are determined based on a Ni intensity, a Co intensity and a Fe intensity each sequentially measured in the depth direction from the surface side of the nickel-cobalt-iron diffusion layer by a radio frequency glow discharge optical emission spectrometry, a content of Co at a specific depth position D, InCo_D, is 8.59% by mass or higher and 65% by mass or lower, a content of Fe at the specific depth position D, InFe_D, is 18% by mass or higher and 70% by mass or lower, a content of Ni at the specific depth position D, InNi_D is 5% by mass or higher and 34.55% by mass or lower, the specific depth position D being a position where the Ni intensity is 0.5% of the maximum value of the Ni intensity, and
• wherein the total content of nickel and cobalt in the nickel-cobalt-iron diffusion layer is 9.0 g/m2 or lower.