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This paper herein studies subcritical crack growth ( SCG) behavior of a perovskite-structured Ba0.5Sr0.5Co0.8Fe0.2O3−δ ( BSCF) as an oxygen transport membrane material. The SCG behavior of BSCF is evaluated by a constant load method and constant stress rate method at room temperature ( RT) and 800°C in air, respectively. The low crack velocity measurements are carried out by ring-on-ring bending tests while the high crack velocity measurements by compact tension tests. The stress rates vary approximately from 0.1012 to 101.2 MPa/min. The fracture stress increases with increasing stress rate at 800°C. The SCG parameter, n, of BSCF is determined to be 24.32 and 13.83 at RT and 800°C in air, respectively. This indicates that BSCF is more susceptible to SCG at 800°C. The strength-probability-time ( SPT) diagram is constructed for design proposes. The stress for a lifetime of 40 years should not exceed 27.21 MPa at RT or 4.53 MPa at 800°C to assure a failure probability below 1%. [ABSTRACT FROM AUTHOR]

Highlights • Failure location in hydrogen embrittled stainless steel joint depends on pre-strain. • Severe strain-induced α′ martensite in the base metal contributes to failure mechanism transition. • Tendency of strain-induced α′ martensitic transformation for the weld metal and base metal is strongly determined by local chemical homogeneity. Abstract The effects of pre-strain on hydrogen embrittlement of 304L K-TIG welded joint were investigated. As pre-strain of joint increased, fracture location of hydrogen-charged joint changed from weld metal to base metal. In low prestrained joints, fracture may be initiated at the sites of clustered dislocations due to hydrogen in weld metal with a high density of pre-existing dislocations. In high prestrained joints, some regions in base metal suffered severe strain-induced α′ martensitic transformation due to Ni depletion bands and cracking occurred at phase boundaries where may provide more sites for the accumulation of hydrogen atoms and dislocations. [ABSTRACT FROM AUTHOR]

The effect of hydrogen on the tensile properties of AISI 304 K-TIG weld metal is investigated in this study. Fractographic analysis demonstrates a transition from quasi-cleavage/cleavage fracture to intergranular fracture in the brittle zone as the hydrogen-charging current density increases, which is attributed to the interplay of crystalline defect, hydrogen atoms, and α′ martensite transformation sites. It is believed that at low current density, α′ martensite nucleates and grows homogeneously in the interior of the grain. At high current density, the stress-induced α′ martensite forms preferentially at the grain boundary, which undergoes severe strain localisation and hydrogen atom segregation. [ABSTRACT FROM AUTHOR]