Study on creep properties of deposited weld metal in nuclear class 316H pipe

Microstructure evolution, creep damage and fracture mechanism of deposited weld metal in muclear class 316H Pipe were studied based on uniaxial creep tests at 525℃ under various stress. The results showed that creep curves consist of three typical stages, including:transient stage, steady-creep stage and accelerated creep regime. Power-law creep dominates the creep deformation behavior of the deposited weld metal. After creep, three types of precipitates can be observed in fractured samples. The Laves phase is considered as the main strengthening phase, which precipitated inside the δ ferrite; the σ phase and the chain-like M₂₃C₆ precipitated around the interface between the δ ferrite and the austenite, facilitating the formation and growth of cavities, which caused the failure for the weld metals. Uniform equiaxed dimples are found in fracture surfaces, indicating that the ductile fracture mechanism occurs in deposited weld metal after creep rupture.