High strength and high formability steel sheet and manufacturing method thereof

Abstract

A high strength and high formability steel sheet contains, by mass % of the steel sheet: greater than 0.020% and less than 0.040% of C; not less than 0.003% and not greater than 0.100% of Si; not less than 0.10% and not greater than 0.60% of Mn; not less than 0.001% and not greater than 0.100% of P; not less than 0.001% and not greater than 0.020% of S; not less than 0.005% and not greater than 0.100% of Al; and greater than 0.0130% and not greater than 0.0170% of N, wherein a remainder is Fe and inevitable impurities, and the steel sheet has: a tensile strength in a rolling direction of not lower than 520 MPa; an Erichsen value of not less than 5.0 mm; and a resin film layer at least on a side to be an inner surface of a can.

1 . A high strength and high formability steel sheet comprising:
 a steel sheet layer comprising, in mass %, greater than 0.020% and less than 0.040% of C;   not less than 0.003% and not greater than 0.100% of Si;   not less than 0.10% and not greater than 0.60% of Mn;   not less than 0.001% and not greater than 0.100% of P;   not less than 0.001% and not greater than 0.020% of S;   not less than 0.005% and not greater than 0.100% of Al;   greater than 0.0130% and not greater than 0.0170% of N;   a remainder being Fe and inevitable impurities; and   a resin film layer on at least one side of the steel sheet layer;   the steel sheet having:   a tensile strength in a rolling direction of not less than 520 MPa; and   an Erichsen value of not less than 5.0 mm.   
     
     
         2 . The steel sheet according to  claim 1 , wherein thickness of the resin film layer is 5 to 100 μm. 
     
     
         3 . A method of manufacturing a high strength and high formability steel sheet comprising:
 forming a slab by continuously casting a steel including, in mass %:
 greater than 0.020% and less than 0.040% of C; 
 not less than 0.003% and not greater than 0.100% of Si; 
 not less than 0.10% and not greater than 0.60% of Mn; 
 not less than 0.001% and not greater than 0.100% of P; 
 not less than 0.001% and not greater than 0.020% of S; 
 not less than 0.005% and not greater than 0.100% of Al; 
 greater than 0.0130% and not greater than 0.0170% of N; and 
 a remainder being Fe and inevitable impurities; 
   performing hot rolling at a slab reheating temperature of not lower than 1150° C.;   coiling at a temperature of not higher than 600° C.;   thereafter performing first cold rolling;   thereafter performing continuous annealing at a soaking temperature of 600 to 700° C. for a soaking period of 10 to 50 seconds;   thereafter performing second cold rolling at a reduction ratio of 8.0 to 15.0%;   attaching a resin film on at least one side of the steel sheet to be an inner surface of a can after forming a surface treatment film by an electrolytic process   such that the steel sheet has a tensile strength in a rolling direction of not less than 520 MPa and an Erichsen value of not less than 5.0 mm.