HIGH TEMPERATURE CYCLIC DEFORMATION BEHAVIOR OF AN ADVANCED AUSTENITIC STAINLESS STEEL (ALLOY 709)

摘要

Advanced structural materials are needed to improve the efficiency, safety and reliability of next-generation nuclear reactors. Preliminary investigation on mechanical properties of a Fe-25wt.%Ni-20Cr austenitic stainless steel (Alloy 709) suggests it might be a potential candidate for Sodium-Cooled Fast Reactor. High temperature cyclic deformation behavior including fatigue and creep-fatigue for the Alloy 709 is considered for design and safety purposes. Strain-controlled low-cycle fatigue tests were performed at strain amplitudes ranging from 0.15% to 0.6% at 750 °C in air following ASTM standard E2714-13, with a constant strain rate of 2 × 10~(-3) s~(-1). In addition, different hold times of 1, 10, 30 and 60 minutes were introduced at the maximum tensile strain to investigate the effect of the creep damage on the fatigue-life at strain amplitude of 0.5% at 750 °C, while 30 and 60 minutes were introduced at the maximum tensile strain at strain amplitude of 0.3% at 750 °C. During continuous cyclic loading, fatigue life is found to decrease with increase in strain amplitude, while the creep-fatigue life is found to decrease with increasing hold time indicating rapid initiation and propagation of cracks. The fractographs of the deformed samples are presented and discussed.