抄録
Static bending test was used to evaluate the toughness of the bearing steel SUJ 2. The results obtained are as follows: (1) Both in oil-quenching and marquenching, maximum hardness was obtained after austenitizing at 900° for 5 min, whereas the toughness decreases remarkably with higher temperature of austenitizing, and above 900° the superiority of marquenching in increasing the toughness diminishes. (2) It is desirable from the effect on toughness that austenitizing time should be as short as possible. (3) Subzero-treatment increases the hardness but reduces the toughness of hardened steel. (4) Oil-quenching and marquenching with or without subzero-treatment followed by tempering up to 200° were compared in their effect on toughness and hardness of heat-treated steels, and it was found that on the hardness level of Rc 59∼61 of these methods, the best properties were obtained by marquenching after austenitizing of 830° 5 mm with or without subzero-treatment followed by tempering, and on the hardness level of Rc 61∼64, by marquenching after austenitizing of 830° 5 min or 860° 5 min followed by tempering.
