Ultra-fine grained steel was developed with alloy design and induction hardening. Bainite structure with finer carbide leads the austenite nucleation site to be increased. Also the Mo precipitates suppress the grain growth according to pinning effect. The automobile components with developed steel with average 5 ㎛ or less grain size were made and evaluated, which are wheel bearing, drive shaft for chassis system and output shaft for transmission. The mechanical properties such as contact fatigue life and torsional strength were improved when developed steel was applied with wheel bearing and drive shaft. The change from carburizing to induction hardening with developed steel for output shaft makes time and cost efficiency.