抄録
In order to evaluate the degree to which thermal cracks in a shaft produced from Ni-Cr-Mo steel would lower the fatigue strength, fatigue tests were carried out at room temperature, 300°C and 500°C under rotating bending.
We have obtained the following facts through the experiments:
(1) The strength reduction factor of thermal crack is about 3.5 at room temperature, 3.3 at 300°C and 2.1 at 500°C. As for the explanation of these results, it appears reasonable to assume that notch sensitivity decreases with the increase of temperature and material around the tip of thermal crack is strengthened through work hardning by repeated load and aging.
(2) The fatigue strength of specimens containing thermal cracks at 500°C could be improved by 50per cent through shot-peening.
