Microstructure and Creep Rupture Characteristics of MarBN Welded Joint

The welded joint of a new kind of martensitic heat resistant steel, namely MarBN, was made by using matching welding rods. Creep rupture tests were carried out in the condition of 650 ℃/120–220 MPa. Microstructure before and after creep rupture tests was observed and hardness tests on the welded joint were performed. Results showed that the microstructure of CGHAZ was finer than those of FGHAZ, ICHAZ and base metal after PWHT. FGHAZ and ICHAZ inherited the coarse lath morphology from base metal but with fine grains in some areas. Before creep, CGHAZ had the highest hardness, while FGHAZ and ICHAZ had the lowest. It was also worth noting that hardness of weld metal was higher than that of base metal before creep. During the process of long-term creep, weld metal experienced the most severe degradation as a result of the most serious ripening of M ₂₃ C ₆ and it eventually fractured in the form of cavity aggregation. Therefore, weld metal was the weakest region throughout the whole welded joint during creep and the welded joint exhibited no tendency towards type IV creep cracking.