Rotating bending fatigue tests were carried out using specimens with a small blind hole for Inconel 718 with different grain sizes, about 18, 88 and 276μm, at room temperature and 500℃ in order to investigate the effects of grain size and temperature on the growth resistance of a fatigue crack. Crack growth rates were determined by the term σ_a^na(a:surface crack length, n:constant), uniquely in all of the materials and at both temperatures. Both of the static strength and the resistance to crack growth were decreased by softening at 500℃. The decrease in the resistance to crack growth was larger than that in the static strength. This was mainly explained from the difference in Young's modulus' at the both temperatures.
