Surface Treated Steel Sheet

Abstract: This surface-treated steel sheet comprises: a base material steel sheet; a plating layer that is formed on the base material steel sheet and that contains 50 mass% or more of Zn and 0.3 mass% or more of Mg; and a chemical conversion coating formed on the plating layer. The chemical conversion coating contains a silicon compound, P and F, and Mg. The average Si concentration in the chemical conversion coating is 10 mass% or more. The chemical conversion coating has, in a region in contact with an interface between the chemical conversion coating and the plating layer, an F-Mg concentrated layer having a Mg concentration of 1.50-40.00 mass% and a F concentration of 0.50-5.00 mass%. The thickness of the F-Mg concentrated layer is 1.0 nm or more. In a region excluding the F-Mg concentrated layer in the chemical conversion coating, the average Mg concentration is less than 0.50 mass% and the average F concentration is less than 0.50 mass%.

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