Steel sheet for crown cap and method for producing the same

Abstract

A steel sheet for a crown cap having sufficient strength and formability suitable for forming crown caps even when reduced in gauge, and a method for producing the steel sheet for a crown cap. The steel sheet for a crown cap having a composition that includes, in terms of % by mass: C: 0.002% or more and 0.010% or less, Si: 0.05% or less, Mn: 0.05% or more and 0.30% or less, P: 0.030% or less, S: 0.020% or less, Al: less than 0.0100%, N: 0.0050% or less, and the balance being Fe and unavoidable impurities. The C content is more than 0.003% when the Al content is 0.005% or more. The yield strength in the rolling direction is 500 MPa or more. The average Lankford value is 1.3 or more.

1 . A steel sheet for crown cap having a composition comprising, in terms of % by mass: C: 0.002% or more and 0.010% or less, Si: 0.05% or less, Mn: 0.05% or more and 0.30% or less, P: 0.030% or less, S: 0.020% or less, Al: less than 0.0100%, N: 0.0050% or less, and the balance being Fe and unavoidable impurities,
 wherein the C content is more than 0.003% when the Al content is 0.005% or more,   a yield strength in a rolling direction is 500 MPa or more, and   an average Lankford value is 1.3 or more, in which
   Average Lankford value=( r   L +2 ×r   D   +r   C )/4, 
   where r L  represents a Lankford value in a direction parallel to the rolling direction, r D  represents a Lankford value in a direction at 45° with respect to the rolling direction, and r C  represents a Lankford value in a direction at 90° with respect to the rolling direction.   
     
     
         2 . The steel sheet for crown cap according to  claim 1 , wherein an absolute value of Δr is 0.40 or less, in which
   Δ r =( r   L −2 ×r   D   +r   C )/2,
 
 where r L  represents a Lankford value in a direction parallel to the rolling direction, r D  represents a Lankford value in a direction at 45° with respect to the rolling direction, and r C  represents a Lankford value in a direction at 90° with respect to the rolling direction. 
 
     
     
         3 . A method for producing a steel sheet for crown cap, the method comprising:
 rough-rolling a slab having the composition according to  claim 1  and finish-rolling the rough-rolled slab at a finish-rolling temperature of 850° C. or higher to obtain a hot-rolled sheet;   coiling the hot-rolled sheet at 450° C. or higher and 750° C. or lower to obtain a coiled sheet;   pickling the coiled sheet to obtain a pickled sheet;   cold-rolling the pickled sheet to obtain a cold-rolled sheet;   annealing the cold-rolled sheet at 650° C. or higher and 790° C. or lower to obtain an annealed sheet; and   cold-rolling the annealed sheet at a rolling reduction of 10% or more and 50% or less when the Al content is 0.003% or less or at a rolling reduction of 20% or more and 50% or less when the Al content is more than 0.003%.