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Abstract: In this paper, the low cycle fatigue properties of JLF-1 steel were studied from room temperature (RT) to 873K in a vacuum condition using engineering size round bar specimens. The fatigue life at elevated temperature was almost the same as that at RT when the life was plotted against the total strain range. But when the life was plotted against the plastic strain range, the temperature effect on fatigue life exceeded the 95% confidence band. Based on TEM analysis, this tendency was caused by the interaction of dislocation changing with temperature, which will affect the possibility of crack initiation. Cyclic softening was observed in the fatigue test at elevated temperature. The cyclic stress–strain curve was obtained from the fatigue stress–strain hysteresis curves at around half life. The cyclic yield point was lower than the static one, especially at 873K. Thus, cyclic softening is a design issue at elevated temperature, which reduces the design margin significantly. [Copyright &y& Elsevier]