Analysis of the creep behaviour of modified P91 (9Cr–1Mo–NbV) welds

The creep response at 600 °C of a P91 (9Cr–1Mo–NbV) steel welded joint was investigated by testing small samples from different weld locations. The microstructure of the weld was analysed by light and transmission electron microscopy. The heat-affected zone material exhibiting a fine-grained structure showed the highest minimum creep-rate values, i.e. the lowest creep strength. The coarse-grained weld metal generally had the greatest creep strength, whereas the parent metal exhibited an intermediate behaviour. The minimum creep-rate dependence on applied stress for weld metal, fine-grained heat-affected zone, and base material was described by means of the conventional power-law equation with a stress exponent close to 15. The experimental results, both in the form of strain vs. time creep curve and of minimum creep rate, were successfully used to simulate the creep response of cross-weld samples.