| 摘要 |
PURPOSE: A manufacturing method of wire rod is provided which reduces surface decarburizing layer generated in high silicon steel and obtains low tensile strength required during cold forming due to high phase fraction of fine graphite powder by forming ferrite decarburizing layer having low carbon solubility in wire rod heating process. CONSTITUTION: The manufacturing method of high silicon added high carbon wire rod with less surface decarburization comprises a step of obtaining a billet comprising 0.65 to 1.50 wt.% of carbon, 2.0 to 4.0 wt.% of silicon, 0.1 to 0.8 wt.% of manganese, 0.01 wt.% or less of phosphorus, 0.01 wt.% or less of sulfur, 0.004 to 0.013 wt.% of nitrogen, 0.005 wt.% or less of oxygen, 0.001 to 0.003 wt.% of boron, 0.005 to 0.03 wt.% of titanium, one or more elements selected from the group consisting of 0.3 to 2.0 wt.% of nickel, 0.01 to 0.5 wt.% of vanadium and 0.01 to 0.5 wt.% of niobium, and a balance of Fe and other impurities, wherein the titanium (Ti), nitrogen (N) and boron (B) satisfy the following relational expressions: 0.5<=Ti/N<=2.0, 2<=N/B<=8, and 1.0<=(Ti+5B)/N<=3.5; a step of heating the billet to a temperature of Ac1 transformation point at a heating rate of 20±5 deg.C/min, heating the billet at a heating rate of 4±2 deg.C/min in the temperature range of Ac1 transformation point to Acm transformation point, heating the billet to a temperature of 1,050±100 deg.C at a heating rate of 15±5 deg.C/min, maintaining the billet in the temperature range of 1,050±100 deg.C for 30 minutes or more, and wire rod rolling the heated billet; a step of coiling the wire rod at a temperature of 860 to 950 deg.C right after wire rod rolling the heated billet; and a step of obtaining a wire rod by air cooling the second cooled wire rod after first cooling the coiled wire rod to a temperature of 770±30 deg.C at a cooling rate of 1.8±0.5 deg.C/sec and second cooling the first cooled wire rod to a temperature of 620±50 deg.C at a cooling rate of 0.4±0.2 deg.C/sec.
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