High-strength wire rod having superior impact toughness and manufacturing method therefor

Abstract

The present invention relates to a high-strength wire rod superior in impact toughness and a manufacturing method therefor and, more particularly, to a high-strength wire rod having superior impact toughness, which can be preferably used as a material for industrial machines or automobiles exposed to various external load environments, and a manufacturing method therefor.

1 . A high-strength wire rod, comprising:
 by wt %, less than 0.05% of C, excluding 0%, 0.05% or less of Si, excluding 0%, 3.0 to 4.0% of Mn, 0.020% or less of P, 0.020% or less of S, 1.0 to 3.0% of Ni, 0.0010 to 0.0030% of B, 0.010 to 0.030% of Ti, less than 0.0030% of N, 0.010 to 0.050% of Al, and a balance of Fe and inevitable impurities,   wherein a microstructure comprises 3 area % or less of a martensite-austenite (MA) constituent, including 0 area %, 2 area % or less of proeutectoid ferrite, including 0 area %, and 95 area % or higher of bainitic ferrite, including 100 area %.   
     
     
         2 . The high-strength wire rod of  claim 1 , wherein the high-strength wire rod satisfies Relational Expression 1 below,
   0.01≤([C]+[Si])/[Ni]≤0.03  [Relational Expression 1]
   where C, Si, and Ni each indicate a content of a respective element by wt %.   
     
     
         3 . The high-strength wire rod of  claim 1 , wherein
 high-strength wire rod satisfies Relational Expression 2 below,
   [Mn]+{5([Ti]−3.5[N])/[B]}≥5.0  [Relational Expression 2]
 
   where Mn, Ti, N, and B each indicate a content of a respective element by wt %.   
     
     
         4 . The high-strength wire rod of  claim 1 , wherein a grain size of a martensite-austenite constituent is 5 μm or less, excluding 0 μm. 
     
     
         5 . The high-strength wire rod of  claim 1 , wherein a content of Ni is 1.2 to 2.8 wt %. 
     
     
         6 . A method of manufacturing a high-strength wire rod, comprising:
 reheating steel comprising less than 0.05% of C, excluding 0%, 0.05% or less of Si, excluding 0%, 3.0 to 4.0% of Mn, 0.020% or less of P, 0.020% or less of S, 1.0 to 3.0% of Ni, 0.0010 to 0.0030% of B, 0.010 to 0.030% of Ti, less than 0.0030% of N, 0.010 to 0.050% of Al, and a balance of Fe and inevitable impurities, by wt %;   obtaining a wire rod by hot-rolling the reheated steel;   primarily cooling the wire rod at a speed of 10 to 20° C./sec to a temperature within a range of Bs° C. to Bs+50° C.;   secondarily cooling the primarily cooled wire rod at a speed of 2 to 5° C./sec a temperature within a range of Bf−50° C. to Bf° C.; and   air-cooling the secondarily cooled wire rod.   
     
     
         7 . The method of  claim 6 , wherein a reheating temperature during the reheating the steel is 950 to 1050° C. 
     
     
         8 . The method of  claim 6 , wherein a finish hot-rolling temperature during the hot-rolling is at is 750 to 850° C.