Cold rolledsteel sheet and method for manufacturing the same

Abstract

A method of manufacturing a cold-rolled steel sheet includes: adding, by weight %, carbon (C) 0.005% or less, nitrogen (N) 0.002 to 0.005%, manganese (Mn) 0.1 to 1.0%, phosphorous (P) 0.005 to 0.1%, niobium (Nb) 0.015 to 0.04%, silicon (Si) 0.30 or less, sulfur (S) 0.02% or less, aluminum 0.001 to 0.03%; adjusting the atomic ratio of Nb/C to 1 or more and the atomic ratio of Al/N to 0.5 to 1.5, homogenizing a steel containing iron (Fe) and elements inevitably contained in manufacturing the steel as the remainder at temperature of 1150 to 1300° C., setting the final hot-rolling temperature to 890 to 950° C. that is over an Ar3 critical point; and hot-winding the hot-rolled steel sheet and cold-rolling the hot-rolled steel sheet at 40 to 80% cold reduction ratio.

1 . A method of manufacturing a cold-rolled steel sheet, comprising:
 adding to iron (Fe), by weight %, carbon (C) 0.005% or less, nitrogen (N) 0.002 to 0.005%, manganese (Mn) 0.1 to 1.0%, phosphorous (P) 0.005 to 0.1%, niobium (Nb) 0.015 to 0.04%, silicon (Si) 0.3% or less, sulfur (S) 0.02% or less, aluminum 0.001 to 0.03% to provide a steel;   adjusting the atomic ratio of Nb/C to 1 or more and the atomic ratio of Al/N to 0.5 to 1.5,   homogenizing the steel at a temperature of 1150 to 1300° C.,   hot-rolling the steel at a final hot-rolling temperature to 890 to 950° C. that is over an Ar3 critical point; and   hot-winding the hot-rolled steel sheet and cold-rolling the hot-rolled steel sheet at 40 to 80% cold reduction ratio.   
     
     
         2 . The method of manufacturing a cold-rolled steel sheet according to  claim 1 , wherein annealing is performed in a range of 750 to 880° C. after the cold-rolling. 
     
     
         3 . The method of manufacturing a cold-rolled steel sheet according to  claim 1 , wherein the hot-winding is performed in a temperature range of 450 to 650° C. 
     
     
         4 . A cold-rolled steel sheet formed of a steel comprising: carbon 0.005% or less, nitrogen (N) 0.002 to 0.005%, manganese (Mn) 0.1 to 1%, phosphorous (P) 0.005 to 0.1%, niobium (Nb) 0.015 to 0.04%, silicon (Si) 0.3% or less, sulfur (S) 0.02% or less, aluminum 0.001 to 0.03%, by weight %, and the remainder of iron (Fe) and elements inevitably contained in manufacturing the steel,
 wherein an atomic ratio of Nb/C is adjusted to 1 or more and an atomic ratio of Al/N is adjusted to 0.5 to 1.5.   
     
     
         5 . A method of manufacturing a steel sheet, the method comprising:
 providing a steel alloy comprising iron (Fe), carbon (C), nitrogen (N), manganese (Mn), phosphorous (P), niobium (Nb), silicon (Si), sulfur (S), aluminum (Al), wherein the atomic ratio of Nb/C is 1 or greater, and the atomic ratio of Al/N is from 0.5 to 1.5 in the steel alloy,   hot-rolling the steel alloy to provide a hot-rolled steel sheet; and   cold-rolling the hot-rolled steel sheet.   
     
     
         6 . The method of  claim 5 , wherein providing the steel alloy comprises:
 providing a raw steel material; and   adding to the raw steel material one or more elements selected from the group consisting of carbon (C), nitrogen (N), manganese (Mn), phosphorous (P), niobium (Nb), silicon (Si), sulfur (S), aluminum (Al).   
     
     
         7 . The method of  claim 6 , wherein Nb is added in such an amount to make the atomic ratio of Nb/C1 or greater, wherein C is not added. 
     
     
         8 . The method of  claim 6 , wherein Nb and C are added in such amounts to make the atomic ratio of Nb/C1 or greater. 
     
     
         9 . The method of  claim 6 , wherein Al and N are added in such amounts to make the atomic ratio of Al/N fall in a range from 0.5 to 1.5. 
     
     
         10 . The method of  claim 6 ,
 wherein C is added in an amount of 0.005 wt. % or less with reference to the total weight of the steel alloy,   wherein N is added in an amount of 0.002 to 0.005 wt. % with reference to the total weight,   wherein Mn is added in an amount of 0.1 to 1.0 wt. % with reference to the total weight,   wherein P is added in an amount of 0.005 to 0.1 wt. % with reference to the total weight,   wherein Nb is added in an amount of 0.015 to 0.04 wt. % with reference to the total weight,   wherein Si added in an amount of 0.3 wt. % or less with reference to the total weight,   wherein S is added in an amount of 0.02 wt. % or less with reference to the total weight,   wherein Al is added in an amount of 0.001 to 0.03 wt. % with reference to the total weight.   
     
     
         11 . The method of  claim 5 , wherein providing the steel alloy further comprises:
 homogenizing the element-added steel material at a temperature between 1150 and 1300° C.   
     
     
         12 . The method of  claim 5 , wherein a final temperature of the hot-rolling is in a range from 890 to 950° C. over an Ar3 critical point. 
     
     
         13 . The method of  claim 5 , wherein a cold reduction ratio of the cold rolling is in a range from 40 to 80%. 
     
     
         14 . A cold-rolled steel sheet manufactured from the method of  claim 6 . 
     
     
         15 . A cold-rolled steel sheet manufactured from the method of  claim 10 .