Abstract
Fatigue crack growth tests were conducted for SUS304 stainless steel in the near-threshold region using single-edge-cracked (SEC) specimens at 350°C, 550°C and 650°C in a vacuum. Crack growth behaviors of SUS304 in a vacuum were compared with those in air to investigate the effect of the environment and oxidation on the behavior of fatigue crack growth in the near-threshold region. It was found that threshold value, ΔKth, was higher than that in air, and that ΔKth at high temperatures reached a maximum value at about 550°C. When the value of Kmax was increased in a threshold condition obtained by using the conventional ΔK-decreasing test, crack growth was observed for ΔK lower than the conventional threshold. Crack growth was also observed after successive increase in Kmax in the newly established subthreshold region in a vacuum as well as in air. In the region below a certain value of ΔK, however, crack no longer grew even after the change of Kmax at 550°C. Discussion was made on the characteristics of the fatigue crack growth threshold.
