Effect of cyclic softening and stress relaxation on fatigue behavior of 2.25Cr1Mo0.25V steel under strain-controlled fatigue-creep interaction at 728 K

Low cycle fatigue behavior of bainitic 2.25Cr1Mo0.25 V steel is studied at 728 K in air by strain amplitudes from 0.2% to 0.6%. Dwell period from 5 s to 600 s, is applied at peak strains to investigate its influence on cyclic response and crack initiation. Microstructural observations are performed to identify the failure mechanism. The dwell periods decrease fatigue endurance by increasing cyclic softening of the steel and incubating incipient fatigue cracks. The stress relaxed during dwell is closely related with fatigue life decreasing. The modified method considered stress relaxation effect estimates low cycle fatigue and fatigue-creep life well.