Abstract
Gigacycle fatigue tests were conducted for SUP7 spring steel using φ7×20 mm and φ3 mm specimens whose risk volumes were 912 and 33 mm^3, respectively. In these tests, all specimens ended in fish-eye fracture whose origin was an Al_2O_3 inclusion. As the result, the φ7×20 mm specimens revealed much lower gigacycle fatigue strength, showing larger inclusions at the fish-eye fracture origins.
