Wire rod having enhanced strength and impact toughness and preparation method for same

Abstract

Provided is a wire rod having enhanced strength and impact toughness. The wire rod includes, by wt %, carbon (C): 0.05% to 0.15%, silicon (Si): 0.2% or less, manganese (Mn): more than 3.5% to 5.0% or less, chromium (Cr): 0.5% to 2.0%, phosphorus (P): 0.020% or less, sulfur (S):0.020% or less, aluminum (Al): 0.010% to 0.050%, iron (Fe) as a residual component, and inevitable impurities. The microstructure of the wire rod includes martensite in an area fraction of 95% or more, and retained austenite (y) as a residual component.

1 . A wire rod having enhanced strength and impact toughness comprising, by wt %, carbon (C): 0.05% to 0.15%, silicon (Si):
 0.2% or less, manganese (Mn): more than 3.5% to 5.0% or less, chromium (Cr): 0.5% to 2.0%, phosphorus (P): 0.020% or less, sulfur (S):0.020% or less, aluminum (Al): 0.010% to 0.050%, iron (Fe) as a residual component, and inevitable impurities,   wherein a microstructure includes martensite in an area fraction of 95% or more, and retained austenite (y) as a residual component.   
     
     
         2 . The wire rod having enhanced strength and impact toughness of  claim 1 , wherein contents of Mn, Cr, and C satisfy Relational Expression 1 below,
   4.0 ≦C ( Mn+Cr ) 5 /50≦9.0.  [Relational Expression 1]
   
     
     
         3 . The wire rod having enhanced strength and impact toughness of  claim 1 , wherein contents of Mn and Si satisfy Relational Expression 2 below,
     Mn/Si≧ 22.  [Relational Expression 2]
   
     
     
         4 . The wire rod having enhanced strength and impact toughness of  claim 1 , wherein the wire rod is provided with any cross section in which a ratio of a maximum concentration [Mn max ] to a minimum concentration [Mn min ] of Mn satisfies Relational Expression 3 below,
   [ Mn   max   ]/[Mn   min ]≦4.  [Relational Expression 3]
   
     
     
         5 . A method of manufacturing a wire rod having enhanced strength and impact toughness, comprising:
 reheating a steel material including, by wt %, C: 0.05% to 0.15%, Si: 0.2% or less, Mn: more than 3.5% to 5.0% or less, Cr: 0.5% to 2.0%, P: 0.020% or less, S: 0.020% or less, Al: 0.010% to 0.050%, Fe as a residual component, and inevitable impurities;   hot rolling the steel material, having been reheated;   cooling the steel material at a rate of 0.2° C./s or higher at a temperature within a range of Mf° C. to Mf-50° C., after the hot rolling; and   air cooling the steel material, having been cooled.   
     
     
         6 . The method of  claim 5 , wherein contents of Mn, Cr, and C satisfy Relational Expression 1 below,
   4.0 ≦C ( Mn+Cr ) 5 /50≦9.0.  [Relational Expression 1]
   
     
     
         7 . The method of  claim 5 , wherein contents of Mn and Si satisfy Relational Expression 2 below,
     Mn/Si≧ 22.  [Relational Expression 2]
   
     
     
         8 . The method of  claim 5 , wherein the reheating is performed at a temperature of 1000° C. to 1100° C. 
     
     
         9 . The method of  claim 5 , wherein finish hot rolling of the hot rolling is performed at a temperature within a range of 850° C. to 950° C.