A 2.25Cr-1Mo steel was subjected to constant amplitude straining in the temperature interval 22 to 550°C. The conventional low-cycle fatigue properties at 22, 350, 450, and 550°C at constant diametral strain rate ˙ϵ_d = 5 × 10⁻³ s⁻¹ were measured. The fatigue hardening-softening curves, cyclic stress-strain curves, and Manson-Coffin curves were obtained at each temperature. A detailed study of the cyclic stress-strain response was performed on a computer-controlled electrohydraulic machine. The temperature dependence of the cyclic yield stress was measured using a multiple step test procedure. The stress-dip procedure in cyclic straining was adopted in order to separate the effective and internal component of the cyclic stress. The dependence of both components on temperature and during fatigue life was measured.

The effective stress component was found to be relatively high in this material and drops only mildly with temperature. The typical temperature dependence of the cyclic stress is due to the internal stress that drops quickly above 450°C and at 550°C is considerably lower than the effective stress. With continued cycling, the decrease of both components contributes to cyclic softening.

Both the cyclic stress-strain response and fatigue life were affected by the strain rate and hold periods within the cycle. The time-dependent effects were studied in detail at 550°C. The frequency dependence of fatigue life at different strain amplitudes was measured. In addition to continuous straining, three basic types of hold times within the cycle with strain or stress relaxations were applied. The experimental data were analyzed, and a set of parameters to correlate the low-cycle fatigue life of the material with various straining conditions was evaluated.