Non-quenched and tempered steel wire with excellent cold forging property and manufacturing method therefor

Abstract

Provided are a non-heat-treated steel wire rod with excellent cold forgeability and a method of manufacturing the same, the non-heat-treated steel wire rod including carbon: 0.20 to 0.40 wt %, silicon: 0.10 to 0.30 wt %, manganese: 1.30 to 1.60 wt %, phosphorus: more than 0 wt % and up to 0.05 wt %, sulfur: more than 0 wt % and up to 0.05 wt %, chromium: 0.02 to 0.30 wt %, nickel: 0.02 to 0.30 wt %, molybdenum: 0.02 to 0.30 wt %, vanadium: 0.01 to 0.15 wt %, niobium: 0.01 to 0.05 wt %, aluminum: 0.005 to 0.060 wt %, titanium: 0.005 to 0.020 wt %, copper: 0.01 to 0.30 wt %, boron: 0.0001 to 0.0020 wt %, nitrogen: 0.005 to 0.015 wt %, and a balance of iron and other unavoidable impurities, wherein a sum of Nb and V is 0.02 to 0.2 wt %, and wherein the non-heat-treated steel wire rod satisfies a tensile strength of 900 MPa or more.

1 . A non-heat-treated steel wire rod, the non-heat-treated steel wire rod comprising: carbon (C): approximately 0.20 wt % to 0.40 wt %, silicon (Si): approximately 0.10 wt % to 0.30 wt %, manganese (Mn): approximately 1.30 wt % to 1.60 wt %, phosphorus (P): more than 0 wt % and up to approximately 0.05 wt %, sulfur(S): more than 0 wt % and up to approximately 0.05 wt %, chromium (Cr): approximately 0.02 wt % to 0.30 wt %, nickel (Ni): approximately 0.02 wt % to 0.30 wt %, molybdenum (Mo): approximately 0.02 wt % to 0.30 wt %, vanadium (V): approximately 0.01 wt % to 0.15 wt %, niobium (Nb): approximately 0.01 wt % to 0.05 wt %, aluminum (Al): approximately 0.005 wt % to 0.060 wt %, titanium (Ti): approximately 0.005 wt % to 0.020 wt %, copper (Cu): approximately 0.01 wt % to 0.30 wt %, boron (B): approximately 0.0001 wt % to 0.0020 wt %, nitrogen (N): approximately 0.005 wt % to 0.015 wt %, and a balance of iron (Fe) and other unavoidable impurities,
 wherein a sum of Nb and V is approximately 0.02 wt % to 0.2 wt %, and   wherein the non-heat-treated steel wire rod satisfies a tensile strength of approximately 900 MPa or more.   
     
     
         2 . The non-heat-treated steel wire rod of  claim 1 , wherein the non-heat-treated steel wire rod comprises a composite precipitate with a diameter of approximately 50 nm or less, and
 wherein the composite precipitate is a composite precipitate comprising one or more selected from Nb, V, Ti, and Al, or one or more selected from composite precipitates comprising TiN, VC, VN, NbC, NbN, AlN, and BN.   
     
     
         3 . The non-heat-treated steel wire rod of  claim 2 , wherein the composite precipitate has an austenite grain size of number 10 or above. 
     
     
         4 . A method of manufacturing a non-heat-treated steel wire rod, the method comprising:
 forming a billet by reheating a steel material comprising carbon (C): approximately 0.20 wt % to 0.40 wt %, silicon (Si): approximately 0.10 wt % to 0.30 wt %, manganese (Mn): approximately 1.30 wt % to 1.60 wt %, phosphorus (P): more than 0 wt % and up to approximately 0.05 wt %, sulfur(S): more than 0 wt % and up to approximately 0.05 wt %, chromium (Cr): approximately 0.02 wt % to 0.30 wt %, nickel (Ni): approximately 0.02 wt % to 0.30 wt %, molybdenum (Mo): approximately 0.02 wt % to 0.30 wt %, vanadium (V): approximately 0.01 wt % to 0.15 wt %, niobium (Nb): approximately 0.01 wt % to 0.05 wt %, aluminum (Al): approximately 0.005 wt % to 0.060 wt %, titanium (Ti): approximately 0.005 wt % to 0.020 wt %, copper (Cu): approximately 0.01 wt % to 0.30 wt %, boron (B): approximately 0.0001 wt % to 0.0020 wt %, nitrogen (N): approximately 0.005 wt % to 0.015 wt %, and a balance of iron (Fe) and other unavoidable impurities, at approximately 1100° C. to 1350° C., wherein a sum of Nb and V is approximately 0.02 wt % to 0.2 wt %;   forming a wire rod by rolling the reheated billet;   cold drawing the wire rod; and   performing cold forging after the cold drawing,
 wherein, in the forming of the wire rod, rolling is performed while heating in a temperature region above an A3 transformation point. 
   
     
     
         5 . The method of  claim 4 , wherein the temperature region above the A3 transformation point is approximately 750° C. to 900° C. 
     
     
         6 . The method of  claim 4 , wherein, in the forming of the wire rod, cooling is performed at a cooling rate of approximately 2° C./s or less after preforming the rolling. 
     
     
         7 . The method of  claim 4 , wherein, in the cold drawing of the wire rod, a drawing reduction rate is approximately 30% to 50%. 
     
     
         8 . The method of  claim 4 , wherein, in the forming of the wire rod, a speed of a conveyor for transporting the wire rod after being rolled is controlled to approximately 0.2 m/s to 0.7 m/s to control an overlap density of the wire rod transported by the conveyor. 
     
     
         9 . The method of  claim 4 , wherein the wire rod manufactured after the cold forging satisfies a tensile strength of approximately 900 MPa or more.