| 摘要 |
PURPOSE:To obtain the title soft wire rod for cold forging capable of omitting spheroidizing annealing by hot-rolling steal having a specified composition with a finishing mill, specifying the final finishing temp. to obtain more than a desired recrystallization grain size, and controlling the cooling conditions. CONSTITUTION:The steel contg., by weight, 0.20-0.60% C, <=0.10% Si, 0.20-0.40% Mn, <=0.020% P, <=0.020% S, 0.20-0.60% Cr, 0.0005-0.0050% B, 0.005-0.030% Ti, 0.010-0.060% Al, <=0.0060% N, and <=0.040% O is treated as follows. Namely, the final finishing temp. is controlled to <=950 deg.C at the time of hot-rolling the steel, and the recrystallized austenite grain size of the rolled wire rod is adjusted to >=11. The hot-rolled steel is cooled at 750-650 deg.C including the ferrite-pearlite transformation range at the cooling rate of <=0.3 deg.C/sec. Consequently, the desired wire rod for cold forging having a granular cementite structure is obtained.
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