| 摘要 |
<p>The present invention provides a steel bar or wire rod for cold forging excellent in ductility after spheroidizing annealing, capable of preventing the steel material from cracking during cold forging, which cracking has conventionally constituted a problem in manufacturing machine structural components by cold forging, and a method of producing the same. Specifically, the steel bar or wire rod for cold forging is characterized by: consisting of a steel containing, in mass, 0.1 to 0.6% of C, 0.01 to 0.5% of Si, 0.2 to 1.7% of Mn, 0.001 to 0.15% of S, 0.015 to 0.05% of Al and 0.003 to 0.025% of N, and having the contents of P and O controlled to 0.035 or less and 0.003% or less, respectively, with the balance consisting of Fe and unavoidable impurities; the area percentage of ferrite in the metallographic structure of the portion from the surface to the depth of 0.15 of its radius being 10% or less, with the rest of the structure consisting substantially of one or more of martensite, bainite and pearlite; and the average hardness of the portion from the depth of 0.5 of its radius to the center being lower than that of its surface layer by HV 20 or more. <IMAGE></p> |
