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The cruciform welded joint is a weak position of filter press to cause fatigue failure under cyclic conditions. In this study, cavitation jet peening (CJP) treatment is proposed to improve the fatigue life of SAF2205 cruciform welded joints. The effects of different CJP treatment positions on the residual stress, microstructure, and microhardness were studied. The results show that different CJP treatment positions have different on residual stresses and fatigue life. The order of the residual stress in fracture position from large to small is the fully treated specimen, untreated specimen, one‐sided treated specimen, and diagonal treated specimen, which is exactly opposite to the order of fatigue life from large to small. After the diagonal CJP treatment, the fatigue life is increased by up to 242.19%, and the residual stress at the weld toe is reduced by more than 80%. A strengthening layer with thicknesses of about 400 μm is formed. [ABSTRACT FROM AUTHOR]

Austenite and duplex stainless steels are widely used in engineering, and the latter exhibits a more excellent combination of mechanical properties and corrosion resistance due to the coexistence of austenite and ferrite and higher nitrogen. However, fatigue failure still threatens their structural integrity. A comprehensive comparison of their cyclic deformation behavior is a major foundation to understand the role of duplex-phase microstructure and nitrogen in the safety assessment of engineering components. Thus, in this paper, the cyclic deformation behavior of fully-austenitic stainless steel 316L and duplex stainless steel 2205 was studied by a series of low cycle fatigue tests with various strain amplitudes, loading rates and tensile holding. A theoretical mechanism diagram of the interaction between nitrogen and dislocation movements during cyclic loads was proposed. Results show that the cyclic stress response of 2205 was the primary cyclic hardening, followed by a long-term cyclic softening regardless of strain amplitudes and rates, while an additional secondary hardening was observed for 316L at greater strain amplitudes. Cyclic softening of 2205 was restrained under slower strain rates or tensile holding due to the interaction between nitrogen and dislocations. The cyclic plasticity of 2205 started within the austenite, and gradually translated into the ferrite with the elevation of the cyclic amplitude, which lead to a decreased hardening ratio with the increase in amplitude and a shorter fatigue life for a given smaller plastic strain amplitude. [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]