Effect of Welding on Gigacycle Fatigue Strength of Austenitic Stainless Steels

抄録

A mercury target vessel, composed of SUS316L stainless steel, is used for the pulsed spallation neutron source and is assembled via gas tungsten arc welding. While in operation, the target vessel suffers approximately 10⁹ loading cycles with a high strain rate of approximately 50 s^-1 because of the proton-beam-induced pressure waves in mercury. The gigacycle fatigue strength for solution annealed SUS316L stainless steels and its welded specimens were investigated through ultrasonic fatigue tests. The experimental results showed that an obvious fatigue limit was not observed at fewer than 10⁹ cycles for the base metal. In the case of no weld defects observed via penetration tests, the fatigue strength of the removed-weld-bead specimen, in which the weld lines were arranged at the center of the specimen, appeared to be slightly higher than that of the base metal. By contrast, as-welded specimens with the weld bead intact showed apparent degradation of the fatigue strength owing to the stress concentration around the weld toe.