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Fiber laser-welded joints of T-250 maraging steel with Cu layer and aging treatment were assessed with respect to tensile properties, microstructure and fractography. The hybrid process based on Cu layer and aging temperature was designed and optimized. All the welded joints fractured in the weld metal region. The approach of electroplating Cu into the weld metal was a practical option. Cu in the weld metal introduced e-Cu precipitates, leading to increase in strength, decreased reverted austenite at the grain boundaries and increased reverted austenite in the matrix, which was beneficial to toughness. High strength-high toughness welded joint was successfully obtained using the hybrid process. The strength and toughness of welded joint were simultaneously over 90% of the parent metal in the regulation window. The main controlling principle of the hybrid process was that the aging temperature (T) and Cu layer (t) meets the following criteria: f ( t ) 2 T f ( t ) 1 , where 587 °C＜T＜610 °C，17.5 µm＜t＜60 µm.

This study reported the evolutionary behavior of macrosegregation induced interface structure during post weld heat treatment (PWHT) and its effect on creep failure in dissimilar metal welds (DMWs) between Ni-based alloy and 10%Cr martensitic steel with Ni-based filler metal. During welding, macrosegregation led to formation of partially mixed beach-like lath martensite interface structure on the steel side. The beach-like structure transformed to rod-like Ni-rich and C-rich martensite accompanied by Ni-depleted and C-depleted martensite/ferrite after PWHT due to partial austenization and diffusion of austenite-stabilizing elements like Ni and C. Interfacial creep failure occurred along the interface between steel and the beach-like interface structure, which was related to creep voids nucleation at the BCC/FCC interface between steel and the beach-like structure during creep at 600 °C. Hence, the relationship between macrosegregation, interface structure and creep failure in the DMWs was clarified.

The creep rupture mechanisms of IN617 were systematically investigated by establishing the relationship between microstructural characteristics and creep performance, including rupture time, percentage elongation, microhardness, and minimum creep rate. The Wilshire equation was employed to extrapolate long-term creep life by normalizing the stress, σ, using the ultimate tensile strength, σTS. The results indicated that at temperatures ≤950 °C, when σ/σYS values were >0.2 (σYS = yield strength), the creep rupture mechanism involved the sliding and migration of recrystallized grain boundaries, leading to matrix softening and necking fractures. When applied stresses ranged from 0.12σTS to 0.2σYS, creep voids along the grain boundaries became a pronounced feature, implying the rupture mechanism of the weakening of the grain boundaries without sufficient secondary-phase pinning. At a low stress level (σ/σTS

In this study, creep rupture behaviors and rupture mechanism of dissimilar metal weld (DMW) between Inconel 617B and modified 9%Cr martensitic heat-resistant steel (hereinafter referred to 9Cr steel) with Inconel 617 filler metal were investigated. Creep tests were carried out at 600 °C and 620 °C in the stress range 130–240 MPa. Optical microscopy (OM), scanning electron microscopy (SEM), Electro-Probe Microanalyzer (EPMA) and micro-hardness test were used to examine the creep rupture behaviors and microstructure characteristics of the DMW. The results indicated that under different creep conditions, the rupture locations varied, including 9Cr base metal (BM), the intercritical heat affected zone (ICHAZ) of 9Cr steel, and the interface between weld metal (WM) and 9Cr steel. The rupture behavior occurring in the 9Cr BM was mainly controlled by plastic deformation, and the growth and coalescence of dimples eventually led to transgranular fracture. The rupture behavior occurring in the ICHAZ was caused by type IV crack due to matrix softening and lack of sufficient precipitates pinning the grain boundaries (GBs). The rupture behavior occurring at the interface was mainly related to the oxide notch forming at the interface. The formation and propagation of the oxide notch resulted in the interfacial failure.