STEEL FOR GEAR HAVING SUPERIOR IMPACT FATIGUE RESISTANCE, AND GEAR USING THE SAME

摘要

PROBLEM TO BE SOLVED: To provide steel for a carburized gear suitable for use in automobiles and various types of industrial machines, which is required to have an excellent impact fatigue strength, and to provide a gear using the same.;SOLUTION: The steel has a composition which comprises, by mass%, 0.16 to 0.30% C, less than 0.40% Si, 0.50% or more Mn, 0.015% or less P, 0.30% or less Cu, less than 2.00% Cr, 0.16 to 0.50% Mo, 0.060 to 0.110% Al, 0.0004% or more B, 0.0065% or less N, at least one element of Ti, Nb and V, as needed, while satisfying the expression (1): I(=14/27×Al+14/10.8×B-N)≥0.03, wherein Al, B and N represent contents (mass%), and the balance Fe with unavoidable impurities. Furthermore, the steel after having been carburized, quenched and tempered satisfies the expression (2): 170≤S(=E/2×D-P/2)≤250, wherein (E) represents the effective depth (mm) of a hardened layer, (D) represents the hardness (HV) of the inner part and (P) represents the depth (μm) of an oxidized layer in a grain boundary.;COPYRIGHT: (C)2008,JPO&INPIT