Manufacturing galvannealed sheets by heat-treating electrolytically finished sheets

Abstract

The invention relates to a method for manufacturing a steel strip with a cathodic corrosion protection coating, in which the steel strip is hot rolled and then cold rolled; the steel strip is subjected to an electrolytic galvanization and after the electrolytic galvanization, the steel strip is heat treated in a bell-type annealing furnace at temperatures of 250° C. to 350° C. for a period of 4 to 48 hours and this produces a zinc/iron layer.

1 . A method for manufacturing a steel strip with a cathodic corrosion protection coating, comprising:
 hot rolling the steel strip and subsequently cold rolling the steel strip;   subjecting the steel strip to an electrolytic galvanization; and   after the electrolytic galvanization, heat treating the steel strip in a bell-type annealing furnace at temperatures of 250° C. to 350° C. for a period of 4 to 48 hours to produce a zinc/iron layer.   
     
     
         2 . The method as recited in  claim 1 , comprising flexibly cold rolling the steel strip in such a way that the steel strip has periodically different thicknesses and/or widths over its length and/or a steel strip with isotropic or higher-strength properties is used. 
     
     
         3 . The method as recited in  claim 1 , wherein before the electrolytic galvanization, the flexibly rolled strip is subjected to a recrystallization annealing at 550° C. to 650° C. in the bell-type annealing furnace or in a continuous annealing furnace. 
     
     
         4 . The method as recited in  claim 1 , wherein a layer thickness of the electrolytically deposited zinc coating is between 2 μm and 10 μm. 
     
     
         5 . The method as recited in  claim 4 , comprising annealing the steel strip in order to convert the zinc layer into a zinc/iron layer in such a way that the zinc/iron layer contains a maximum of 30% iron.