Patent ID: 6602359
Filing Date: 2003-08-05
Classification: C21D,C22C

Abstract:
A steel bar or wire rod for cold forging excellent in ductility after spheroidizing annealing, having a chemical composition comprising, in mass,0.1 to 0.65% 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 0.1% of Al, 0.0005 to 0.007% of B, and the restricted elements of0.035% or less of P, 0.01% or less of N and 0.003% or less of O, with the balance consisting of Fe and unavoidable impurities, characterized in that: the area percentage of ferrite structure is 10% or less at the portion from the surface to a depth of 0.15 times the radius of the steel bar or wire rod; the other portion consists substantially of one or more of martensite, bainite and pearlite; and further the average hardness of the portion from the depth of 0.5 times its radius to its center is less than the hardness of its surface layer (the portion from the surface to the depth of 0.15 times the radius) by HV 20 or more.