Cyclic plastic response and fatigue life in superduplex 2507 stainless steel

Superduplex 2507 type steel has been subjected to symmetric cyclic loading with constant strain rate and constant plastic strain amplitude or sinusoidal cyclic loading with constant stress amplitude at room temperature in a wide interval of stress and plastic strain amplitudes. Fatigue hardening/softening curves were recorded and compared for both types of loading. Cyclic stress–strain curves and fatigue life curves in the form of Coffin–Manson curve and Wöhler curve using both loading regimes were evaluated and compared. The analysis of the hysteresis loop shape was used to determine the contribution of the effective stress and to find the distribution of critical internal stresses in both phases of the steel. The typical internal dislocation structure in both phases was documented. The cyclic response of the material was discussed in relation to the dislocation structure developed in cyclic straining in austenitic and ferritic phases.