STEEL FOR GEAR HAVING EXCELLENT DEDENDUM BENDING FATIGUE CHARACTERISTIC AND FACIAL PRESSURE FATIGUE CHARACTERISTIC AND GEAR

摘要

PROBLEM TO BE SOLVED: To provide steel for a gear in which its dedendum bending fatigue strength is higher than that of the conventional gear, further, facial pressure fatigue characteristics are excellent, and mass production is possible and to provide a gear produced by the same steel. SOLUTION: The gear is composed of the one obtained by forming steel having a composition containing, by mass, 0.10 to 0.35% C, 0.5 to 2.0% Si, 0.2 to 1.0% Mn, 0.01 to 0.50% Ni, 0.5 to 2.5% Cr, 0.01 to 1.00% Mo, 0.005 to 0.200% Al and 0.001 to 0.200% V, and in which the Ac3 temperature parameter is 850 to 940 deg.C, the ideal critical diameter DI is 40 to 400 mm, the carbon equivalent Ceq is =1.100, and the temper softening resistance parameter is =100 into a gear shape by forging or machine working, in which the content of retained austenite from the surface layer of the gear to the depth position of 100 μm when carburizing treatment or carbo-nitriding treatment is performed is =40 vol.%, also, the structure of the core part as a noncarburized part is composed of the dual phase one of ferrite and martensite, and the ratio of ferrite therein is 10 to 45 area %.