STEEL PRODUCT FOR BEARING AND METHOD FOR HEAT TREATING THE SAME

摘要

PURPOSE: A steel product for bearing is provided which improves durable performance and load power under normal lubricating conditions and alien substance and heating environments considering operating environment of bearing operated under large load conditions and poor environment, and a method for heat treating the same is provided. CONSTITUTION: The method for heat treating a steel product for bearing comprises a carbonizing process (S11) of carburizing the steel product for bearing at a temperature of 930 to 970 deg.C at a decarburizing gas atmosphere having carbon potential of 0.9 to 1.2% for a certain period of time according to hardening depth by injecting a steel product for bearing containing 0.27 to 0.33 wt.% of C, 0.30 to 0.60 wt.% of Si, 0.90 to 1.30 wt.% of Mn, 1.0 to 1.30 wt.% of Cr, 0.10 to 0.30 wt.% of V, 200 to 400 ppm of Al, 100 to 200 ppm of N and a balance of Fe into a heat treatment furnace; a carbonitriding process (S12) of carbonizing and nitriding the steel product for bearing at a temperature of 870 to 910 deg.C for 2 to 5 hours by additionally injecting 2 to 5 vol.% of ammonia gas into carburizing gas of the decarburizing gas atmosphere (carbon potential of 0.9 to 1.2%) of the carbonizing process; first quenching process (S13) of first quenching the steel product for bearing by rapidly cooling the steel product for bearing from the temperature of 870 to 910 deg.C of the carbonitriding process; second quenching process (S14) of second quenching the steel product for bearing by rapidly cooling the heated steel product for bearing after heating the first quenched steel product for bearing to a temperature of 830 to 860 deg.C in a heat treatment furnace having carbon potential of 0.6 to 1.0%; and a tempering process (S15) of slowly cooling the heated steel product for bearing after heating the second quenched steel product for bearing to a temperature of 160 to 220 deg.C in the heat treatment furnace.