Method of manufacturing Graphite Steel Rod for machine structural use having lower decarburized surf

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PURPOSE : A method for manufacturing graphite steel wire rod for machine structure having lower surface decarburization property is provided to reduce thickness of a surface decarburization layer by substantially reducing decarburization rate on the surface of a billet in a wire rod rolling process. CONSTITUTION : A method for manufacturing graphite steel wire rod for machine structure having lower surface decarburization property comprises : a step of obtaining a continuously cast bloom comprising 0.30 to 0.70 wt.% of carbon(C), 2.0 to 4.0 wt.% of silicon(Si), 0.1 to 1.0 wt.% of manganese(Mn), 0.01 to 0.15 wt.% of phosphorous(P), 0.01 wt.% or less of sulfur(S), 0.001 to 0.05 wt.% of selenium(Se), 0.001 to 0.03 wt.% of titanium(Ti), 0.001 to 0.003 wt.% of boron(B), 0.002 to 0.01 wt.% of aluminum(Al), 0.004 to 0.008 wt.% of nitrogen(N), 0.005 wt.% or less of oxygen(O), one or more selected from the group consisting of 0.05 to 1.0 wt.% of nickel(Ni), 0.01 to 0.5 wt.% of copper(Cu), 0.0001 to 0.05 wt.% of calcium(Ca), 0.0005 to 0.008 wt.% of zirconium(Zr) and 0.001 to 0.05 wt.% of rare earth metal and the balance being Fe and other impurities, the Ti, N, B and Al satisfying the following relation : 2.0<=(Ti+5B+Al)/N<=5.5, the Mn, Se and S satisfying the following relation : 1.0<=(Mn/5+Se)/5S<=3.0; a step of piling and air cooling the bloom to a temperature of 600±100 deg.C; a step of obtaining a billet by reheating and rolling the reheated bloom in a temperature range of 1, 260±30 deg.C for 100±20 minutes; and a step of heating the billet to a heating temperature of 1, 050±50 deg.C in a heating rate of 10 deg.C/min or more, maintaining the heated billet in the temperature range for 30 minutes or more and rolling the billet to obtain a wire rod. © KIPO 2006