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• 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]

• >Synthetical effect of material inhomogeneity and welding defect on fatigue behavior. • >New structure strain method including heterogeneous plasticity and stress singularity. • >Evolution of fatigue mode with geometric configurations and cyclic amplitudes. • >A damage tolerance-based fatigue design concept to guide manufacture of welded joints. This paper performed experimental and analytical investigations on the synthetical effect of material inhomogeneity and welding defects on the fatigue behavior of 2205 duplex stainless steel cruciform welded joints. A series of experiments were performed, including microstructure characterization by the electron back-scattered diffraction, fatigue mechanical tests assisted by digital image correlation technique and fracture morphology observations by scanning electron microscope. Results show that fatigue life and failure location of cruciform welded joints depended heavily on their geometric configurations for lower cyclic amplitudes. However, with the elevation of loading, material inhomogeneity played a greater roles, leading to the change of fatigue failure mode with both geometric configuration and cyclic stress amplitude. To quantize the effects of welding defects and material inhomogeneity, a modified structure strain method was proposed by considering the heterogeneous plastic properties, to accurately predict both fatigue lifetime and failure location of cruciform welded joints at both low and high cycles fatigue. Lastly, a damage tolerance-based fatigue design method was discussed to guide the highly-reliable manufacture and damage detection of duplex stainless steel cruciform welded joints in the engineering. [ABSTRACT FROM AUTHOR]

• A multiscale model was proposed to accurately predict the heterogeneous and multiscale elasto-plastic properties of 2205 DSS welded joints. • The contribution of Peierls–Nabarro stress, solid solution strengthening, grain/phase boundary, and dislocations density on the macro-mechanical properties (YS and UTS) was quantified. • The evolution of heterogeneous micro-mechanical responses with two constitutive phases with the elevation of loads was predicted accurately. • The banded GBAs and its adjacent ferrite were more prone to plastic-deformed. This work aims to reveal the inherent dependency between the heterogeneous microstructure induced by the metallurgical transformation during welding of 2205 duplex stainless steel (DSS) and its macroscopic and microscopic elasto-plastic properties by experiments and models. A multiscale model was developed by combining a macro-constitutive model incorporating the physically-based yield strength and a crystal plasticity model considering both the micro-mechanical properties of two phases and their realistic morphology. The results show that the heterogeneous macro-mechanical properties of base metal (BM), heat affected zone (HAZ), and weld material (WM), as well as their micro-mechanical responses related to phase morphology, ratio, and grain size, can be accurately predicted. The contribution of Peierls–Nabarro stress, solid solution strengthening, grain/phase boundary, and dislocations density on macro-yield and tensile strengths was quantified, and WM was proven to have greater yield and tensile strengths due to the greater contribution of grain refinement and solid solution strengthening. In addition, a transition mechanism of the deformation-bearing phase from austenite to ferrite with the increase of load was proved, and the banded grain boundary austenite (GBA) and its adjacent ferritic grains were prone to plastic-deformation. This work can be used as guidance of structure integrity assessment and welding process optimization for the engineering components of DSS. [ABSTRACT FROM AUTHOR]

In this study, the microstructure characteristics and formation mechanism of DSS (duplex stainless steel) multi-pass weld joints were firstly investigated in terms of the OM (optical microscope) and EBSD (electron back-scattered diffraction) observation, and a series mechanical tests, including the monotonic tensile tests assisted by the DIC (digital image correlation) observation and stress-controlled fatigue tests, were subsequently performed to clarify the intrinsic correlation between mechanical behavior and microstructure. The fatigue fracture morphologies and cracks propagation behavior were analyzed by the OM and SEM (scanning electron microscope) observation. The results show that the significant ferritiszation and determined precipitations were found at the HAZ (heat-affected zone), whereas the austenite was dominating at weld filler zone due to the more formation of the IGA (intragranular austenite). A nearly balance phase ratio was obtained at weld back and cap zones, but the strip GBA (grain boundary austenites) was connected into piece along thickness direction. The monotonic tensile strength of weld joints was higher than that of the based materials due to the refined-grains structures, and the final rupture occurred at the BM (based material) zone. However, the fatigue lifetimes of weld joints were much shorter than that of based materials for the same cyclic amplitude. The fatigue cracks preferred to nucleate at weld back or cap passes although where phase ratio was approximately balance. The austenitic grains which were connected into pieces accelerated the initiation of fatigue cracks. Apart from maintaining phases balance and avoiding detrimental precipitation, the alternative distribution of austenite and ferrite should also be obtained in the engineering. [ABSTRACT FROM AUTHOR]