Surface-treated steel sheet and method of producing the same

A method of producing a surface-treated steel sheet having:

• a steel sheet;
• a metallic Cr layer disposed on at least one surface of the steel sheet;
• and a Cr oxide layer disposed on the metallic Cr layer, the method comprising:
• an electrolyte preparation process to prepare an electrolyte containing trivalent chromium ions;
• a cathodic electrolysis treatment process to subject a steel sheet to cathodic electrolysis treatment in the electrolyte;
• a water washing process to subject the steel sheet after the cathodic electrolysis treatment to water washing at least once;
• and
• thereby producing the surface-treated steel sheet having:
• a water contact angle of 50° or less;
• and
• a total atomic ratio of K, Na, Mg, and Ca adsorbed on the surface to Cr of 5% or less,
• wherein, in the electrolyte preparation process, the electrolyte is prepared by:
• mixing a trivalent chromium ion source, a carboxylic acid compound, and water;
• and
• adjusting the pH to 4.0 to 7.0 and the temperature to 40° C. to 70° C., and
• in the water washing process,
• at least the last water washing uses water with an electrical conductivity of 100 μS/m or less.