2008 年 2008 巻 53 号 p. 9-12
Accidental temperature rise will cause a significant decrease in the fatigue limit of the steel which has been subjected to the multiple surface treatment of vacuum carbonitriding and double shot peening. The phenomenon was investigated by the volume fraction of retained austenite and residual stress level altered by the tempering temperature. Based on the knowledge of this study, the new methodology to overcome the degradation was proposed. The residual stress and high hardness introduced by vacuum carbonitriding and double shot peening were decreased by tempering with the temperature of 573 K and above due to the decomposition of the retained austenite. The phenomenon makes fatigue limit to the 56 % reduced level. It turned out that the residual stress did not decrease by heating at 573 K, if the residual stress is introduced by double shot peening after tempering with high temperature where the retained austenite was completely decomposed.