| 摘要 |
PURPOSE: A method for manufacturing wire rods for bolts having superior spheroidizing heat treatment properties is provided to shorten the time for spheroidizing heat treatment and improve productivity by adding Ni and W to steel and appropriately controlling hot rolling and cold wire drawing. CONSTITUTION: The method comprises the processes of reheating a steel slab comprising 0.2 to 0.7 wt.% of C, 0.5 to 1.5 wt.% of Si, 0.3 wt.% or less of Mn, 0.01 wt.% or less of P, 0.03 wt.% or less of S, 0.5 to 1.5 wt.% of Ni, 0.2 to 1.0 wt.% of W and a balance of Fe and other inevitably contained impurities to a temperature of 950 to 1150 deg.C; manufacturing a wire rod or round bar by hot rolling the reheated steel slab to the final rolling conditions of 800 to 950 deg.C; cold rolling the wire rod or round bar to a forming amount of 5% or more, and reheating the cold rolled wire rod or round bar in the temperature range of 630 to 730 deg.C; and air cooling the wire rod or round bar to an ordinary temperature after maintaining the reheated wire rod or round bar for more than 2 hours.
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