| 摘要 |
The present invention employs a hot-rolled bar member having a chemical composition that contains 0.05 to 0.30% of C, 0.30 to 0.60% of Si, 0.40 to 1.0% of Mn, 0.008 to under 0.040% of S, 1.60 to 2.00% of Cr, 0.1% or less of Mo, 0.025 to 0.05% of Al, 0.010 to 0.025% of N, 0.003% or less of Ti, and 0.0001 to 0.0050% of Bi, with the remainder comprising Fe and impurities, and the amount of P and O among the impurities being 0.025% or less and 0.002% or less, respectively, wherein the structure is formed from ferrite-pearlite or ferrite-pearlite-bainite, and satisfies formula (1). Formula (1): 1.70≤Cr+2×Mo≤2.10 |
