Creep Crack Propagation Behavior of Different Regions in Domestic Vanadium Steel Welded Joint

Taking the domestically produced 2.25Cr-1Mo-V vanadium steel welded joint as the research object, creep crack propagation tests were conducted on the base metal, weld, and heat affected zone at 550 ℃ and different initial stress intensity factors (19.04, 17.57, 16.40, 14.64, 13.47 MPa · m^0.5). The creep crack propagation behavior of different regions in the welded joint was studied, and the applicability of stress intensity factor and C^* parameter to characterize creep crack propagation rate was investigated. The fracture morphology was observed. The results show that as the initial stress intensity factor increased, the creep fracture lives of the base metal, weld, and heat affected zone were all shortened, and the normalized steady-state creep crack propagation rate increased. Under the same initial stress intensity factor, the creep fracture life of the weld was the longest and the normalized steady-state creep crack propagation rate was the smallest , indicating that the weld had the strongest resistance to creep crack propagation and the best creep performance; the creep fracture life of the heat affected zone was the shortest and the normalized steady-state creep crack propagation rate was the highest. The curves of normalized creep crack propagation rate and stress intensity factor of different regions in welded joint all showed a“V”shape, corresponding to the initiation, stable propagation, and accelerated propagation stages of creep cracks. The distribution of stress intensity factor and normalized creep crack propagation rate exhibited significant dispersion. The C^* parameter had a strong linear relationship with the normalized creep crack propagation rate, and the distribution of C^* parameter and normalized creep crack propagation rate was concentrated. With the increase of initial stress intensity factor, the fracture mode of base metal, weld and heat affected zone changed from intergranular or transgranular fracture to intergranular/transgranular mixed fracture.