In order to predict long-term behavior of a high-creep resistant low-carbon Type 316L stainless steel under low-cycle fatigue with long hold times, a series of tests of fatigue relaxation was undertaken at 550, 600, 650, and 700°C for medium strain ranges (Δε_t = 0.7, 1.2, and 1.6 percent). Hold times up to 5 h were introduced at the maximum tensile strain. It has been shown that a reduction of fatigue life occurred, generally associated with intergranular cracking when hold times increased. A maximal effect was observed at 600°C.

Different methods for extrapolating results for very long hold times, such as those encountered on fast breeder reactor components (∼1000 h) were proposed. These methods were based on a time-temperature equivalence comparable to those used for extrapolating creep rupture data. A correlation between reduction of fatigue life with the amount of stress relaxation during hold times was also used. Predictions by these methods are compared with ASME N47 fatigue design curves.