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 comprising, by wt %, carbon (C): 0.05% to 0.15%, silicon (Si): 0.2% or less, manganese (Mn): 3.0% to 4.0%, phosphorus (P): 0.020% or less, sulfur (5):0.020% or less, boron (B): 0.0010% to 0.0030%, titanium (Ti): 0.010% to 0.030%, nitrogen (N): 0.0050% or less, aluminum (Al): 0.010% to 0.050%, iron (Fe) as a residual component thereof, and other unavoidable impurities. A microstructure includes bainitic ferrite in an area fraction of 90% or more, and a martensite/austenite (M/A) constituent as a residual component thereof.

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): 3.0% to 4.0%, phosphorus (P): 0.020% or less, sulfur (S): 0.020% or less, boron (B): 0.0010% to 0.0030%, titanium (Ti): 0.010% to 0.030%, nitrogen (N): 0.0050% or less, aluminum (Al): 0.010% to 0.050%, iron (Fe) as a residual component thereof, and other unavoidable impurities,
 wherein a microstructure includes bainitic ferrite in an area fraction of 90% or more, and a martensite/austenite (M/A) constituent as a residual component thereof.   
     
     
         2 . The wire rod having enhanced strength and impact toughness of  claim 1 , wherein the wire rod additionally comprises chromium (Cr): less than 0.3%. 
     
     
         3 . The wire rod having enhanced strength and impact toughness of  claim 1 , wherein the content of manganese (Mn), titanium (Ti), boron (B), and nitrogen (N) satisfies Relational Expression 1,
   Mn+5(Ti−3.5N)/B≧5.0.   [Relational Expression 1]
   
     
     
         4 . The wire rod having enhanced strength and impact toughness of  claim 1 , wherein the content of manganese (Mn) and silicon (Si) satisfies Relational Expression 2,
   Mn/Si≧18.   [Relational Expression 2]
   
     
     
         5 . The wire rod having enhanced strength and impact toughness of  claim 1 , wherein the wire rod is provided with an arbitrary cross section in which a ratio of a maximum concentration [Mn max ] and a minimum concentration [Mn min ] of manganese satisfies Relational Expression 3,
   [Mn max ]/[Mn min ]≦3.   [Relational Expression 3]
   
     
     
         6 . The wire rod having enhanced strength and impact toughness of  claim 1 , wherein a grain size of the martensite/austenite (M/A) constituent is 5 μm or less. 
     
     
         7 . A method of preparing a wire rod having enhanced strength and impact toughness comprising:
 reheating a steel material including, by wt %, carbon (C): 0.05% to 0.15%, silicon (Si): 0.2% or less, manganese (Mn): 3.0% to 4.0%, phosphorus (P): 0.020% or less, sulfur (S): 0.020% or less, boron (B): 0.0010% to 0.0030%, titanium (Ti): 0.010% to 0.030%, nitrogen (N): 0.0050% or less, aluminum (Al): 0.010% to 0.050%, iron (Fe) as a residual component thereof, and other unavoidable impurities;   hot rolling the steel material having been reheated;   cooling the steel material at a rate of 0.1° C./s to 2° C./s in a temperature within a range of Bf° C. to Bf−50° C., after the hot rolling; and   air cooling the steel material having been cooled.   
     
     
         8 . The method of preparing a wire rod having enhanced strength and impact toughness of  claim 7 , wherein the steel material additionally includes chromium (Cr): less than 0.3%. 
     
     
         9 . The method of preparing a wire rod having enhanced strength and impact toughness of  claim 7 , wherein the content of manganese (Mn), titanium (Ti), boron (B), and nitrogen (N) satisfies Relational Expression 1,
   Mn+5(Ti−3.5N)/B≧5.0.   [Relational Expression 1]
   
     
     
         10 . The method of preparing a wire rod having enhanced strength and impact toughness of  claim 7 , wherein the content of manganese (Mn) and silicon (Si) satisfies Relational Expression 2,
   Mn/Si≧18.   [Relational Expression 2]
   
     
     
         11 . The method of preparing a wire rod having enhanced strength and impact toughness of  claim 7 , wherein the reheating is performed at a temperature of 1000° C. to 1100° C. 
     
     
         12 . The method of preparing a wire rod having enhanced strength and impact toughness of  claim 7 , wherein finish hot rolling, of the hot rolling, is performed at a temperature within a range of 850° C. to 950° C.