Surface-treated steel sheet and production method therefor

Abstract

Provided is a surface-treated steel sheet that can be produced without using hexavalent chromium and has excellent corrosion resistance at BPA-free painted worked part. A surface-treated steel sheet comprises: a steel sheet; and a chromium-containing layer disposed on a surface of the steel sheet on at least one side, wherein when the chromium-containing layer is observed from a surface direction, linear regions in which an element smaller in atomic number than chromium is concentrated are present, and the number of the linear regions is 5.0 or more per 100 nm.

1 . A surface-treated steel sheet comprising:
 a steel sheet; and   a chromium-containing layer disposed on a surface of the steel sheet on at least one side,   wherein when the chromium-containing layer is observed from a surface direction, linear regions in which an element smaller in atomic number than chromium is concentrated are present, and   the number of the linear regions is 5.0 or more per 100 nm.   
     
     
         2 . The surface-treated steel sheet according to  claim 1 , wherein the linear regions have a mesh-like connected structure. 
     
     
         3 . The surface-treated steel sheet according to  claim 2 , wherein a standard deviation of an equivalent circular diameter of the mesh is 30 nm or less. 
     
     
         4 . The surface-treated steel sheet according to  claim 2 , wherein average roundness of the mesh is 0.5 to 1.0. 
     
     
         5 . The surface-treated steel sheet according to  claim 1 , wherein a chromium coating weight of the chromium-containing layer is 40.0 mg/m 2  to 500.0 mg/m 2  per one side. 
     
     
         6 . The surface-treated steel sheet according to  claim 1 , wherein a chromium oxide coating weight of the chromium-containing layer is 40.0 mg/m 2  or less per one side. 
     
     
         7 . The surface-treated steel sheet according to  claim 1 , wherein an area ratio of a crystalline region when the chromium-containing layer is observed from the surface direction is 30% or less. 
     
     
         8 . A production method for a surface-treated steel sheet that includes: a steel sheet; and a chromium-containing layer disposed on a surface of the steel sheet on at least one side, the production method comprising:
 bringing the steel sheet into contact with an aqueous solution containing sulfate ions, and holding the steel sheet in a state in which 1.0 g/m 2  to 30.0 g/m 2  of the aqueous solution is present on the surface of the steel sheet for 0.1 seconds to 20.0 seconds; and   subjecting the steel sheet to cathodic electrolysis treatment in an electrolytic solution containing 0.05 mol/L or more of trivalent chromium ions.   
     
     
         9 . The production method for a surface-treated steel sheet according to  claim 8 , wherein the electrolytic solution is prepared by mixing a trivalent chromium ion source, a carboxylic acid compound, and water, adjusting pH to 4.0 to 7.0, and adjusting temperature to 40° C. to 70° C. 
     
     
         10 . The surface-treated steel sheet according to  claim 3 , wherein average roundness of the mesh is 0.5 to 1.0. 
     
     
         11 . The surface-treated steel sheet according to  claim 2 , wherein a chromium coating weight of the chromium-containing layer is 40.0 mg/m 2  to 500.0 mg/m 2  per one side. 
     
     
         12 . The surface-treated steel sheet according to  claim 3 , wherein a chromium coating weight of the chromium-containing layer is 40.0 mg/m 2  to 500.0 mg/m 2  per one side. 
     
     
         13 . The surface-treated steel sheet according to  claim 4 , wherein a chromium coating weight of the chromium-containing layer is 40.0 mg/m 2  to 500.0 mg/m 2  per one side. 
     
     
         14 . The surface-treated steel sheet according to  claim 2 , wherein a chromium oxide coating weight of the chromium-containing layer is 40.0 mg/m 2  or less per one side. 
     
     
         15 . The surface-treated steel sheet according to  claim 3 , wherein a chromium oxide coating weight of the chromium-containing layer is 40.0 mg/m 2  or less per one side. 
     
     
         16 . The surface-treated steel sheet according to  claim 4 , wherein a chromium oxide coating weight of the chromium-containing layer is 40.0 mg/m 2  or less per one side. 
     
     
         17 . The surface-treated steel sheet according to  claim 2 , wherein an area ratio of a crystalline region when the chromium-containing layer is observed from the surface direction is 30% or less. 
     
     
         18 . The surface-treated steel sheet according to  claim 3 , wherein an area ratio of a crystalline region when the chromium-containing layer is observed from the surface direction is 30% or less. 
     
     
         19 . The surface-treated steel sheet according to  claim 4 , wherein an area ratio of a crystalline region when the chromium-containing layer is observed from the surface direction is 30% or less.