Wire rod and part with improved delayed fracture resistance, and methods for manufacturing same

Abstract

Disclosed are wire rods and parts with improved delayed fracture resistance, and methods for manufacturing the same. The wire rod with improved delayed fracture resistance according to the present disclosure contains, by wt %, 0.15-0.30% of C, 0.15-0.25% of Si, 0.95-1.35% of Mn, 0.030% or less of P, 0.030% or less of S, 0.015-0.030% of Ti, 0.0010-0.0040% of B, 0.0010-0.0080% of N, and Fe and inevitable impurities as the balance, and satisfies formula 1 of 2.0≤5.5×[Si]+[Mn]≤2.4, where [Si] and [Mn] represent the contents (wt %) of the corresponding elements.

1 . A wire rod with improved delayed fracture resistance, comprising, by wt %, 0.15-0.30% of C, 0.15-0.25% of Si, 0.95-1.35% of Mn, 0.030% or less of P, 0.030% or less of S, 0.015-0.030% of Ti, 0.0010-0.0040% of B, 0.0010-0.0080% of N, and Fe and inevitable impurities as the balance, and satisfying formula 1:
   2.0≤5.5×[Si]+[Mn]≤2.4  [Formula 1]
   wherein [Si] and [Mn] represent the contents (wt %) of the corresponding elements.   
     
     
         2 . The wire rod according to  claim 1 , which satisfies formula 2:
   1.0<[Ti]/3.42[N]≤2.0  [Formula 2]
   wherein [Ti] and [N] represent the contents (wt %) of the corresponding elements.   
     
     
         3 . The wire rod according to  claim 1 , wherein the size of TiN inclusions is 15 m or smaller. 
     
     
         4 . A method for manufacturing a wire rod with improved delayed fracture resistance, comprising:
 a step of finish-rolling a steel material comprising, by wt %, 0.15-0.30% of C, 0.15-0.25% of Si, 0.95-1.35% of Mn, 0.030% or less of P, 0.030% or less of S, 0.015-0.030% of Ti, 0.0010-0.0040% of B, 0.0010-0.0080% of N, and Fe and inevitable impurities as the balance and satisfying formula 1 at 880-980° C.; and   a step of winding at 830-930° C.
   2.0≤5.5×[Si]+[Mn]≤2.4  [Formula 1]
 
   wherein [Si] and [Mn] represent the contents (wt %) of the corresponding elements.   
     
     
         5 . The method for manufacturing a wire rod according to  claim 4 , wherein the steel material satisfies formula 2:
   1.0<[Ti]/3.42[N]≤2.0  [Formula 2]
   wherein [Ti] and [N] represent the contents (wt %) of the corresponding elements.   
     
     
         6 . A method for manufacturing a part with improved delayed fracture resistance, comprising:
 a step of drawing a wire rod manufactured according to  claim 4 ;   a step of spheroidization heat-treating the drawn wire rod at 745-770° C.;   a step of heating the spheroidization heat-treated drawn wire rod at 870-940° C.;   a step of quenching the spheroidization heat-treated drawn wire rod at 50-80° C.; and   a step of tempering the quenched part at 400-600° C.   
     
     
         7 . A part with improved delayed fracture resistance, comprising, by wt %, 0.15-0.30% of C, 0.15-0.25% of Si, 0.95-1.35% of Mn, 0.030% or less of P, 0.030% or less of S, 0.015-0.030% of Ti, 0.0010-0.0040% of B, 0.0010-0.0080% of N, and Fe and inevitable impurities as the balance, and satisfying formula 1:
   2.0≤5.5×[Si]+[Mn]≤2.4  [Formula 1]
   wherein [Si] and [Mn] represent the contents (wt %) of the corresponding elements.   
     
     
         8 . The part according to  claim 7 , which satisfies formula 2:
   1.0<[Ti]/3.42[N]≤2.0  [Formula 2]
   wherein [Ti] and [N] represent the contents (wt %) of the corresponding elements.   
     
     
         9 . The part according to  claim 7 , which comprises, by volume fraction, 0.3-2% of a retained austenite structure and a residual tempered martensite structure. 
     
     
         10 . A method for manufacturing a part with improved delayed fracture resistance, comprising:
 a step of drawing a wire rod manufactured according to  claim 5 ;   a step of spheroidization heat-treating the drawn wire rod at 745-770° C.;   a step of heating the spheroidization heat-treated drawn wire rod at 870-940° C.;   a step of quenching the spheroidization heat-treated drawn wire rod at 50-80° C.; and   a step of tempering the quenched part at 400-600° C.