抄録
The authors proposed previously the method for predicting the fatigue limit of smoothed specimens made of tufftrided steel from the hardened depth h and the distance from surface to center of specimen a. It was expected that the linear relation should hold between the improvement ratio of fatigue limit σw·t/σw·nt and h/(a-h) according to the prediction method. In case of the tufftrided steel supersaturated with nitrogen in the matrix, the linear relation was observed between these two quantities as expected and the validity of the method was clarified.
On the other hand, it has been already reported that the fatigue limit of tufftrided steel decreases with the precipitation of nitrides of Fe4N. In this paper, the applicability of this prediction method is investigated on the tufftrided steel which has the nitrides of Fe4N.
The results obtained are summarized as follows:
(1) The fatigue limit of tufftrided steel decreases with the increase of nitride, and the decrease stops when the precipitation of nitride is perfectly completed. Its fatigue limit is still larger than that of non-tufftrided steel.
(2) The linear relation is also observed between σw·t/σw·nt and h/(a-h) on the tufftrided steel which contains nitrides. Consequently, it is concluded that the prediction method proposed by the authors can be applied regardless of the condition of nitrogen. However, the linear relation equations differ depending upon the condition of nitrogen.
