Patent ID: 8733199

Claim:
A gear, comprising: a disk portion; and a plurality of tooth portions that are circumferentially formed in a discrete manner on the disk portion, wherein the gear is subjected to carburizing treatment and then quenching treatment by high-density energy heating after formation of the gear, wherein a raw material steel of the gear has the following chemical composition: C: 0.1% to 0.40% by mass; Si: 0.35% to 3.0% by mass; Mn: 0.1% to 3.0% by mass; Cr: less than 0.2% by mass; Mo: 0.1% or less by mass; P: 0.03% or less by mass; S: 0.15% or less by mass; Al: 0.05% or less by mass; N: 0.03% or less by mass; and Fe and unavoidable impurities: remainder, the gear includes a first quenched-hardened layer that has a higher C concentration than the C concentration of the raw material steel and includes a martensitic structure, the first quench-hardened layer being formed throughout (i) a surface layer portion of each of the tooth portions and (ii) a surface layer portion of a tooth root portion that is a portion between the tooth portions on the disk portion, the gear includes a second quench-hardened layer that has a C concentration the same as the C concentration of the raw material steel and includes a martensitic structure, the second quench-hardened layer being formed throughout (i) an interior tooth portion encompassing the entire interior volume of each of the tooth portions other than the portion serving as the first quench-hardened layer, (ii) a portion of the disk portion lying below the first quench-hardened layer of the tooth root portion, and (iii) a portion of the disk portion lying under each of the tooth portions directly below the interior tooth portion, and the gear includes an unquenched region of the disk portion that has a C concentration the same as the C concentration of the raw material steel and includes no martensitic structure, the unquenched region of the disk portion lying deeper than the second quench-hardened layer.