Surface-treated steel sheet and method of producing same

Abstract

Provided is a surface-treated steel sheet that can be produced without the use of hexavalent chromium and that combines excellent film corrosion resistance, coating corrosion resistance, film wet adhesion, coating secondary adhesion, and weldability. At least one side of the surface-treated steel sheet includes a Ni-containing layer, a metallic Cr layer on the Ni-containing layer, and an oxidized Cr layer on the metallic Cr layer. The water contact angle is 50° or less, and the total atomic ratio to Cr of K, Na, Mg, and Ca adsorbed on the surface is 5.0% or less.

1 . A surface-treated steel sheet comprising:
 a steel sheet;   a Ni-containing layer disposed on at least one surface of the steel sheet;   a metallic Cr layer disposed on the Ni-containing layer; and   a Cr oxide layer disposed on the metallic Cr layer, 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 a surface to Cr of 5.0% or less.   
     
     
         2 . The surface-treated steel sheet according to  claim 1 , wherein the Ni-containing layer has a Ni coating weight of 200 mg/m 2  or more and 2000 mg/m 2  or less per side of the steel sheet. 
     
     
         3 . The surface-treated steel sheet according to  claim 1 , wherein the metallic Cr layer has a Cr coating weight of 2 mg/m 2  or more and less than 40 mg/m 2  per side of the steel sheet. 
     
     
         4 . The surface-treated steel sheet according to  claim 1 , wherein the Cr oxide layer has a Cr coating weight of 0.1 mg/m 2  or more and 15.0 mg/m 2  or less per side of the steel sheet. 
     
     
         5 . The surface-treated steel sheet according to  claim 1 , having an atomic ratio of Ni on the surface of the surface-treated steel sheet to Cr of 100% or less. 
     
     
         6 . A method of producing a surface-treated steel sheet comprising a steel sheet; a Ni-containing layer disposed on at least one surface of the steel sheet; a metallic Cr layer disposed on the Ni-containing layer; and a Cr oxide layer disposed on the metallic Cr layer, the method comprising:
 an electrolyte preparation process of preparing an electrolyte containing trivalent chromium ions;   a cathodic electrolysis treatment process of cathodic electrolysis treatment in the electrolyte of the steel sheet comprising the Ni-containing layer on at least one surface; and   a water washing process of at least one water wash of the steel sheet after the cathodic electrolysis treatment,   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 adjusting the temperature to 40° C. to 70° C., and in the water washing process, 
 water having an electrical conductivity of 100 μS/m or less is used in at least the last water wash. 
   
     
     
         7 . The surface-treated steel sheet according to  claim 2 , wherein the metallic Cr layer has a Cr coating weight of 2 mg/m 2  or more and less than 40 mg/m 2  per side of the steel sheet. 
     
     
         8 . The surface-treated steel sheet according to  claim 2 , wherein the Cr oxide layer has a Cr coating weight of 0.1 mg/m 2  or more and 15.0 mg/m 2  or less per side of the steel sheet. 
     
     
         9 . The surface-treated steel sheet according to  claim 3 , wherein the Cr oxide layer has a Cr coating weight of 0.1 mg/m 2  or more and 15.0 mg/m 2  or less per side of the steel sheet. 
     
     
         10 . The surface-treated steel sheet according to  claim 7 , wherein the Cr oxide layer has a Cr coating weight of 0.1 mg/m 2  or more and 15.0 mg/m 2  or less per side of the steel sheet. 
     
     
         11 . The surface-treated steel sheet according to  claim 2 , having an atomic ratio of Ni on the surface of the surface-treated steel sheet to Cr of 100% or less. 
     
     
         12 . The surface-treated steel sheet according to  claim 3 , having an atomic ratio of Ni on the surface of the surface-treated steel sheet to Cr of 100% or less. 
     
     
         13 . The surface-treated steel sheet according to  claim 4 , having an atomic ratio of Ni on the surface of the surface-treated steel sheet to Cr of 100% or less. 
     
     
         14 . The surface-treated steel sheet according to  claim 7 , having an atomic ratio of Ni on the surface of the surface-treated steel sheet to Cr of 100% or less. 
     
     
         15 . The surface-treated steel sheet according to  claim 8 , having an atomic ratio of Ni on the surface of the surface-treated steel sheet to Cr of 100% or less. 
     
     
         16 . The surface-treated steel sheet according to  claim 9 , having an atomic ratio of Ni on the surface of the surface-treated steel sheet to Cr of 100% or less. 
     
     
         17 . The surface-treated steel sheet according to  claim 10 , having an atomic ratio of Ni on the surface of the surface-treated steel sheet to Cr of 100% or less.