| 摘要 |
PURPOSE:To greatly enhance the fatigue strength of a high strength gear used in the drive system of an automobile without the gear being turned into an assembly structure at a one rank higher level, by quenching a part in the vicinity of a tooth trough including a tooth root fillet and thereafter by subjecting the part to a cutting process. CONSTITUTION:After surface treatment when a high hardness material is subjected to a cutting process by use of a cutting tool made of CBN, ceramic, ultra-hard steel, etc., Martensite plastic flow occurs to effect metal flow which incurrs work hardening so that the structure of the material is turned into Martensite. In such a condition, the hardened part is applied with a high compression residual stress so that its fatigue strength is enhanced, and therefore, it is difficult to be cracked. Further, when it is subjected to a caburizing quenching process, an carburized abnormal layer is created so that its outer surface grain boundary is oxidized. However, when it is subjected to a cutting process after quenching, such an abnormal layer is removed and the roundness of a tooth root fillet section 3 is increased. That is, when the part in the vicinity of a tooth through including a tooth root fillet section is subjected to a cutting process after quenching, the tooth surface side of a hypoid gear tooth 1 is cut, stress concentration upon loading is relatively relaxed. |
