Effect of Cyclic Strain Rate on Environmental Fatigue Behaviors of SA508 Gr.1a Low Alloy Steel in 310°C Deoxygenated Water

Abstract

The low cycle fatigue tests of SA508 Gr.1a low alloy steel in 310oC deoxygenated water were conducted to investigate the effect of cyclic strain rate on the environmentally assisted cracking (EAC) mechanisms. The flattened striations and the blunt crack tip, which indicate the occurrence of the slip dissolution/oxidation, were mainly observed for the specimen tested at 0.008 %/s. On the other hand, the brittle cracks and the blunt main crack with microcracks, which are the evidences of the hydrogen-induced cracking (HIC), were observed for the specimens tested at 0.04 and 0.4 %/s. Through this study, it is thought that the slip dissolution/oxidation dominantly contributes to the reduction in the fatigue life at a strain rate of 0.008 %/s and the HIC is mainly responsible for the reduction in the fatigue life at strain rates of 0.04 and 0.4 %/s.

Effects of oxide on fatigue crack growth behaviour of type 347 stainless steel in PWR water conditions

“…The HIC is another important mechanism to decrease the fatigue life of austenite stainless steels in PWR water . The main source of hydrogen is the hydrogen gas purging process to reduce the DO content in the PWR water.…”

“…Environmental fatigue tests have mostly been carried out to evaluate the low cycle fatigue life of low alloy steels and austenitic stainless steel in the range of temperature, dissolved oxygen (DO), strain rate and the water flow rate of the PWR water condition . It has been reported that the fatigue life of austenitic stainless steel can be reduced in PWR water conditions where the DO content is extremely low . A probable mechanism is a hydrogen‐induced cracking (HIC) where the hydrogen ions are generated by an electrochemical reaction and diffused into the metal at the crack tip.…”