Wire rod having superior hydrogen delayed fracture resistance, method for manufacturing same, high strength bolt using same and method for manufacturing bolt

Abstract

The present invention relates to a wire rod used in bolts for automobile engines, for example, and more specifically to a wire rod having an improved resistance to hydrogen delayed fracture, to a manufacturing method for same, to a bolt using same and a method for manufacturing the bolt. Provided are a high strength wire rod having a superior resistance to hydrogen delayed fracture and a method for manufacturing same, a high strength bolt using the wire rod and a method for manufacturing same, wherein. the wire rod comprises, 0.3-0.7 wt % C, 0.05-2.0 wt % Si, 0.7-1.5 wt % Mn, 0.01-0.1 wt % Ni, and 30-70 ppm La, and the remainder thereof is comprised by Fe and inevitable impurities.

1 . A wire rod having superior hydrogen delayed fracture resistance and comprising C: 0.3 to 0.7 wt %, Si: 0.05 to 2.0 wt %, Mn: 0.7 to 1.5 wt %, La: 30 to 70 ppm, Ni: 0.01 to 0.1 %, and a remainder configured of Fe and inevitable impurities. 
     
     
         2 . The wire rod of  claim 1 , wherein the wire rod includes a lanthanum (La)-based, a nickel (Ni)-based, or a LaNi-based precipitate. 
     
     
         3 . The wire rod of  claim 2 , wherein an aspect ratio of the precipitate is 1.2 to 2.0. 
     
     
         4 . The wire rod of  claim 2 , wherein an average circular-equivalent diameter of the precipitate is 100 to 400 nm. 
     
     
         5 . The wire rod of  claim 2 , wherein the precipitate is at least one of LaNi 5 , LaPO 4  and La 2 O 2 S. 
     
     
         6 . A method for manufacturing a wire rod having superior hydrogen delayed fracture resistance, the method comprising:
 heating steel including C: 0.3 to 0.7 wt %, Si: 0.05 to 2.0 wt %, Mn: 0.7 to 1.5 wt %, La: 30 to 70 ppm, Ni: 0.01 to 0.1%, and a remainder configured of Fe and inevitable impurities to a temperature of Ae3+150° C. to Ae3+250° C.;   cooling the heated steel at a rate of 5 to 15° C./s and rolling, the steel at a temperature of Ae3+50° C. to Ae3+150° C. to manufacture a wire rod; and   cooling the rolled wire rod to 600° C. or less at a rate of 0.5 to 3° C./s.   
     
     
         7 . The method of  claim 6 , wherein the heating is performed for 30 minutes to one and a half hours, 
     
     
         8 . A bolt comprising C: 0.3 to 0.7 wt %, Si: 0.05 to 2.0 wt %, Mn: 0.7 to 1.5 wt %, La: 30 to 70 ppm, Ni: 0.01 to 0.1%, and a remainder configured of Fe and inevitable impurities, and having a tensile strength of 1200 MPa or greater and superior hydrogen delayed fracture resistance. 
     
     
         9 . The bolt of  claim 8 , wherein a microstructure of the bolt includes a lanthanum (La)-based, a nickel (Ni)-based, or a LaNi-based precipitate having an aspect ratio of 1.2 to 2.0. 
     
     
         10 . The bolt of  claim 9 , wherein the aspect ratio of the precipitate is 1.2 to 2.0. 
     
     
         11 . The bolt of  claim 9 , wherein an average circular-equivalent diameter of the precipitate is 100 to 400nm, 
     
     
         12 . The bolt of  claim 9 , wherein the precipitate is at least one of LaNi 5 , LaPO 4  and La 2 O 2 S. 
     
     
         13 . A method for manufacturing a bolt having superior hydrogen delayed fracture resistance, the method comprising:
 heating steel including C: 0.3 to 0.7 wt %, Si: 0.05 to 2.0 wt %, Mn: 0.7 to 1.5 wt %, La: 30 to 70 ppm, Ni: 0.01 to 0.1%, and a remainder configured of Fe and inevitable impurities to a temperature of Ae3+150° C. to Ae3+250° C.;   cooling the heated steel at a rate of 5 to 15° C./s and rolling the steel at a temperature of Ae3+50° C. to Ae3+150° C. to manufacture a wire rod;   cooling the rolled wire rod to 600 ° C. or less at a rate of 0.5 to 3° C./s; and   bolt-forming using the cooled wire rod;   performing a heat treatment on the formed bolt at a temperature of 850 to 950° C.; and   performing quenching after the heat treatment, and then performing tempering at a temperature of 300 to 500° C.   
     
     
         14 . The method of  claim 13 , wherein the heating is performed for 30 minutes to one and a half hours.