Fatigue failure mechanism of duplex stainless steel welded joints including role of heterogeneous cyclic hardening/softening: Experimental and modeling.

• The correlation among heterogeneous microstructure, cyclic hardening/softening and fatigue failure behavior was analyzed extensively. • The fracture location was changed with the fatigue amplitude due to the amplitude-dependent and heterogeneous cyclic hardening/softening of BM and WM. • A modified cyclic constitutive model was proposed to precisely predict the heterogeneous cyclic mechanical response and failure location for both stress-controlled and strain-controlled conditions. This work performed experimental and modeling investigations on the fatigue failure mechanism of duplex stainless steel welded joints, and the correlation among heterogeneous microstructure, cyclic hardening/softening and fatigue failure behavior was analyzed extensively. A series of experiments including the characterization of microstructure by the electron back-scattered diffraction observation and fatigue mechanical tests assisted by digital image correlation technique were performed. The results show that at the lower stress amplitudes (approximately 520 MPa), the fatigue failure occurred in the weld metal, while it shifted to the base metal at higher amplitudes. Due to the grain refinement, the strain amplitude of weld metal was lower than that of base metal, particularly at the higher amplitudes, leading to the final failure at the base metal. However, at the lower amplitudes, due to the effect of Kurdjumov-Sachs orientation relationship at the weld metal, its cyclic softening behavior was much drastic than that of base metal, resulting in the overshoot of strain amplitude during fatigue process and finial rupture at the weld metal. A cyclic constitutive model was developed by considering the amplitude-dependent and heterogeneous cyclic hardening/softening, to accurately predict the cyclic mechanical response and fatigue failure location for both stress-controlled and strain-controlled conditions. This work can be used as guidance of structure integrity assessment and life prediction for the engineering components of duplex stainless steel. [ABSTRACT FROM AUTHOR]