Steel for case hardening bearing excellent in toughness and rolling fatigue life in quasi-high temperature region

摘要

A case hardening bearing steel having an excellent rolling contact fatigue life in intermediate temperature, in addition, excellent toughness at room temperature is provided. Specific means for solving the problems are as follows. The composition contains, by mass percent, C of 0.15 to 0.30 mass percent, Si of 0.5 to 2.0 mass percent, Mn of 0.3 to 2.0 mass percent, Cr of 1.3 to 2.5 mass percent, Mo of 0.3 to 1.0 mass percent, and O of not more than 0.0012 mass percent in a range where (Si+Mo)>=1.0 mass percent is satisfied, and contains iron and inevitable impurities as remnant; the maximum size of oxide nonmetallic inclusion is not more than 12.5 mum when examined area is 320 mm²; number of the oxide nonmetallic inclusion having a diameter of equivalent circle of 3 mum or more is not more than 250 when the examined area is 320 mm²; in addition, C density of an outer layer is adjusted to be in a range from 0.7 to 1.2 mass percent by carburization.