Abstract
It is known that high strength steel will cause the characteristic internal fracture called Fish eye fracture in very high cycle region. From this, in order to use high strength steel more efficiently and more safely, the elucidation of the mechanism of the Fish eye fracture produced in low stress and long-life and construction of the lifetime evaluation method of Fish eye fracture are desired. In this study, we did ΔK decrease fatigue test under vacuum environment, and examined the relation between internal fracture in very high cycle region and extremely slow fatigue crack growth behavior under vacuum environment. As a result, the influence of material strength was not seen under vacuum environment. Moreover, opening stress increases with increases of maximum stress.
