700℃에서의 Type 316L 스테인리스강의 저사이클 피로 거동

Abstract

Thermal energy storage system is one of the energy storage systems that use thermal method. Large-scale thermal energy storage system performance test facility being developed by KAERI is designed to be operated in high-temperature environment of 700℃. Considering the heat resistance characteristic, economy and ease of acquisition, it is expected that Type 316L austenitic stainless steel will be used as structural material for AHX, heat storage tank and hot leg. The design of a thermal energy storage system operating at high temperature in the creep region must take into account low cycle fatigue and creep-fatigue damage due to cyclic loads under heat ip, cool down and transient loads. However, in previous studies, it was investigated that there was no study on low cycle fatigue behavior at 700℃, which is the design temperature of a large-scale thermal energy storage system performance test facility being developed at the KAERI. Therefore, in this study, an experimental studies were conducted to determine fatigue strengths and low cycle fatigue behavior of Type 316L stainless steel at 700℃. Fully reversed strain controlled low cycle fatigue tests were conducted with total strain ranges of 0.4%, 0.6%, 0.8%, 1.0% and 1.2%, under a constant strain rate of 10^-3/s at 700℃. As the total strain range increased, the fatigue life of KAERI plate and TIG plate decreased. The cyclic stress response behavior of both the KAERI plate and TIG plate in all total strain ranges showed initial cyclic hardening behavior, followed by a saturation area for a certain period of time and then failure after cyclic softening. Through the hysteresis loop, a non-Masing behavior in which the steps of the tensile load do not match was observed. The fatigue life of the KAERI plate and TIG plate of Type 316L stainless steel predicted by the Coffin-Manson-Basquin model and strain energy density method was found to be in good agreement with the experimental data. In the prediction of fatigue life, the strain energy density method was shown to be reliable for less than 10^4, and the Coffin-Manson-Basquin model was reliable for more than 10^4.