STEEL FOR COLD FORGING/NITRIDING, STEEL MATERIAL FOR COLD FORGING/NITRIDING, AND COLD FORGED/NITRIDED MEMBER

摘要

A steel for cold forging/nitriding, having a chemical composition comprising, in mass%, 0.10 to 0.15% of C, 0.02% or more and less than 0.10% of Si, more than 0.90% and up to 2.50% of Mn, 0.030% or less of P, 0.050% or less of S, 0.80 to 2.0% of Cr, 0.05 to 0.50% of V, 0.01 to 0.07% of Al, 0.0080% or less of N and 0.0030% or less of O, optionally containing a specified amount of at least one element selected from Mo, Cu, Ni, Ti, Nb, Zr, Pb, Ca, Bi, Te, Se and Sb, with the remainder being Fe and impurities, wherein the following equations are fulfilled: [35 ≤ Mn/S ≤ 200], [20 ≤ (669.3×log_eC-1959.6×log_eN-6983.3)×(0.067×Mo+0.147×V) ≤ 80], [140×Cr+125×Al+235×V ≥ 160] and [150 ≤ 511×C+33×Mn+56×Cu+15×Ni+36×Cr+5×Mo+134×V ≤ 200]. The steel for cold forging/nitriding has excellent cold forging performance and excellent machinability after cold forging, and can impart high core hardness, high surface hardness and a large effective case depth to a cold forged/nitrided member. Therefore, the steel for cold forging/nitriding can be used suitably as a base steel for a cold forged/nitrided member.