Low cycle fatigue behavior of hot-bent 347 stainless steels in a simulated PWR environments

Abstract

Low cycle fatigue (LCF) behavior of hot-bending 347 SS for each position in a simulated PWR environments was studied for the application of surge line pipe. To evaluate the effect of hot-bending on the LCF behavior of 347 SS, LCF tests were performed in room temperature (RT) air and simulated pressurized water reactor (PWR) water environments. The LCF life of 347 SS was much shorter in PWR water than in RT air. Meanwhile, LCF life of hot-bent 347 SS was somewhat longer than that of the as-received condition both in RT air and PWR water. Microstructure analysis showed the development of dislocation structure near niobi-um carbide particles and increase in dislocation density for the hot-bent 347 SS, which acted as a barrier to dislocation movement and suppressed the serrated flow in hysteresis loop during the LCF test. Therefore, the degree of hardening was greater for the hot-bent 347 SS. In addition, a clear correlation was found between the degree of hardening and LCF life. In conclusion, the development of dislocation structure near niobium carbide along with increase in dislocation density could have contributed to the longer LCF for the hot-bent 347 SS in both RT air and PWR water.