Deformation behavior, microstructure evolution, and rupture mechanism of the novel G115 steel welded joint during creep

To promote the wide application of the G115 steel in ultra-supercritical (USC) power plants, creep deformation, microstructure evolution and rupture mechanism of the G115 welded joint were systematically investigated. The fabricated G115 welded joint exhibits superior creep strength to the P92 or MARBN steels. The deformation behaviors are analyzed by the Norton's power law, proving that the deformation mechanism is closely associated with the stress levels. During short-term creep under higher stress, the weld metal (WM) and heat-affected zone (HAZ) exhibit outstanding microstructure stability, and the rupture occurs within the base metal (BM) due to the lath fracture. While, during long-term creep under lower stress, the brittle Type IV cracking occurs within the inter-critical heat-affected zone (ICHAZ) or fine-grained heat-affected zone (FGHAZ) due to the formed micro-voids along boundaries, obviously deteriorating the creep strength. The weld strength reduction factors are calculated under different stresses, and prove that synergistic action of back stress and dislocation motion can enhance the creep resistance of the G115 welded joint. Additionally, the allowable service stress of G115 weldments should be designed according to the creep strength of the welded joints under expected performance life.