Surface Treated Steel Sheet

Abstract: This surface-treated steel sheet comprises: a steel sheet; a zinc-based plating layer formed on the surface of the steel sheet; and a chemical conversion layer formed on the surface of the zinc-based plating layer. The chemical conversion layer contains Si, C, O, and P. In the chemical conversion layer, the C concentration is 20.0 mass% or more, the O concentration is 15.0 mass% or more, the Si concentration is 10.0 mass% or more, the P concentration is 0.10 mass% or more. When the thickness of the chemical conversion layer is defined as t, when a surface layer region is defined as a range where the starting point is the surface of the chemical conversion layer and the end point is a position located t/10 from the surface of the chemical conversion layer in the thickness direction, when an interface-side region is defined as a range where the starting point is a position located 9t/10 from the surface of the chemical conversion layer in the thickness direction and the end point is the interface between the chemical conversion layer and the zinc-based plating layer, and when an intermediate region is defined as a region interposed between the surface layer region and the interface-side region, the maximum value of the P concentration in the surface layer region is 1.5-5.0 fold of the average P concentration in the intermediate region.

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