Steel wire rod having excellent cold heading quality and hydrogen delayed fracture resistance, method of manufacturing the same, and mehod of manufacturing bolt using the same

Abstract

Provided are a high-strength, high-manganese steel wire rod having excellent cold heading quality and not requiring spheroidizing and quenching-tempering treatments during manufacturing a bolt and a method of manufacturing a bolt using the steel wire rod. The method of manufacturing a steel wire rod includes heating a steel containing 12 to 25 wt % of Mn within a temperature range of 1100° C. to 1250° C., hot rolling the heated steel within a temperature range of 700° C. to 1100° C., and cooling the hot rolled steel to a temperature of 200° C. or less and cold caliber rolling or drawing to manufacture a steel wire rod.

1 . A method of manufacturing a steel wire rod having excellent cold heading quality and hydrogen delayed fracture resistance, comprising:
 heating a steel containing about 12 wt % to about 25 wt % of manganese (Mn) within a temperature range of about 1100° C. to about 1250° C.;   hot rolling the heated steel within a temperature range of about 700° C. to about 1100° C.; and   cooling the hot rolled steel to a temperature of 200° C. or less and cold caliber rolling or drawing to manufacture a steel wire rod.   
     
     
         2 . The method according to  claim 1 ,
 wherein the steel comprises about 12 wt % to about 25 wt % of manganese (Mn), about 0.5 wt % to about 1.0 wt % of carbon (C), about 1.0 wt % to about 2.0 wt % of aluminum (Al), residual iron (Fe), and unavoidable impurities.   
     
     
         3 . The method according to  claim 1 ,
 wherein the cold caliber rolling or drawing is performed at a reduction of area range of about 10% to about 70%.   
     
     
         4 . The method according to  claim 3 ,
 wherein the cold caliber rolling is performed at a reduction of area range of about 30% to about 90%.   
     
     
         5 . A steel wire rod having excellent cold heading quality and hydrogen delayed fracture resistance comprising about 12 wt % to about 25 wt % of manganese (Mn),
 wherein a microstructure of the steel wire rod comprises a face centered cubic austenitic structure and a <112>{111} twin system.   
     
     
         6 . The steel wire rod having excellent cold heading quality and hydrogen delayed fracture resistance according to  claim 5 ,
 wherein the steel wire rod comprises a total of twelve twin systems in four <112> orientations and three {111} planes of a lattice and four twin variants are formed in one plane.   
     
     
         7 . The steel wire rod having excellent cold heading quality and hydrogen delayed fracture resistance according to  claim 5 ,
 wherein a composition of the steel wire rod comprises about 12 wt % to about 25 wt % of manganese (Mn), about 0.5 wt % to about 1.0 wt % of carbon (C), about 1.0 wt % to about 2.0 wt % of aluminum (Al), residual iron (Fe), and unavoidable impurities.   
     
     
         8 . A method of manufacturing a bolt, comprising:
 heating a steel containing about 12 wt % to about 25 wt % of manganese (Mn) within a temperature range of about 1100° C. to about 1250° C.;   hot rolling the heated steel within a temperature range of about 700° C. to about 1100° C.;   cooling the hot rolled steel to a temperature of 200° C. or less and cold caliber rolling or drawing to manufacture a steel wire rod;   cold heading the steel wire rod to manufacture a bolt head; and   performing a heat treatment on the cold forged steel wire rod within a temperature range of about 400° C. to about 600° C.   
     
     
         9 . The method according to  claim 8 ,
 wherein the steel comprises about 12 wt % to about 25 wt % of manganese (Mn), about 0.5 wt % to about 1.0 wt % of carbon (C), about 1.0 wt % to about 2.0 wt % of aluminum (Al), residual iron (Fe), and unavoidable impurities.   
     
     
         10 . The method according to  claim 8 ,
 wherein the cold caliber rolling or drawing is performed at a reduction of area range of about 10% to about 70%.   
     
     
         11 . The method according to  claim 8 ,
 wherein the cold caliber rolling is performed at a reduction of area range of about 30% to about 90%.   
     
     
         12 . The method according to  claim 8 ,
 wherein the heat treatment is performed for about 10 minutes or less.