Environmentally-Assisted Fatigue Behavior of 316 Stainless Steels in Simulated PWR Primary Environment: Strain Holding, Zn-Addition, and Their Combined Effect

Low cycle fatigue (LCF) tests of type 316 stainless steel (SS) were conducted in simulated pressurized water reactor (PWR) environments to evaluate the effect of zinc (Zn) content and peak strain holding. The LCF lives of 316 SS increased about 2 to 3 times in PWR environments with Zn addition and peak strain holding (Zn-PWR_hold condition). Their combined effect was investigated by using cyclic hardening behavior, dislocation structure analysis, and oxide layer observation. The cyclic behavior in Zn-PWR_hold condition showed general primary hardening behavior but quite longer softening behavior than other test conditions. Also, the dislocation density was decreased with Zn addition and increased again with peak strain holding. The Zn penetrates into the oxide layer at the crack tip and modifies the oxide characteristics, which results in improvement of corrosion resistance.