Process of manufacturing high-strength cold rolled steel sheets

Abstract

A process of manufacturing high-strength cold rolled steel sheets containing 0.5 to 2.0 mass % silicon includes a pickling step of thermally annealing a steel sheet in a non-oxidizing atmosphere and thereafter pickling the steel sheet to dissolve away 0.5 g/m 2 to less than 2.0 g/m 2 of the steel sheet, and an electroplating step of electroplating the surface of the pickled steel sheet with zinc under such conditions that a coating mass of 100 to 5000 mg/m 2 is obtained.

1 .- 3 . (canceled) 
     
     
         4 . A process of manufacturing high-strength cold rolled steel sheets containing 0.5 to 2.0 mass % silicon, comprising:
 a pickling step of thermally annealing a steel sheet in a non-oxidizing atmosphere and thereafter pickling the steel sheet to dissolve away 0.5 g/m 2  to less than 2.0 g/m 2  of the steel sheet, and   an electroplating step of electroplating the surface of the pickled steel sheet with zinc under such conditions that a coating mass of 100 to 5000 mg/m 2  is obtained.   
     
     
         5 . The process according to  claim 4 , wherein the non-oxidizing atmosphere is obtained by introducing a mixture gas containing nitrogen and hydrogen,
 the hydrogen content in the non-oxidizing atmosphere is not more than 10 vol %, and   the temperature of heating during the thermal annealing is not more than 900° C.   
     
     
         6 . The process according to  claim 4 , further comprising an aqueous solution contact step of bringing the steel sheet after the electroplating step into contact with a P-containing aqueous solution having a concentration of not less than 0.001 g/L at a temperature of the P-containing aqueous solution of not less than 30° C. 
     
     
         7 . The process according to  claim 5 , further comprising an aqueous solution contact step of bringing the steel sheet after the electroplating step into contact with a P-containing aqueous solution having a concentration of not less than 0.001 g/L at a temperature of the P-containing aqueous solution of not less than 30° C.