A method for manufacturing a blank part in Ni-base superalloy, wherein an alloy is prepared and heat treatments are conducted characterized in that: the said superalloy contains at least a total of 2.5% of Nb and Ta; heat treatment is conducted comprising a plurality of steps: a first step at between 850 and 1000° C. held for at least 20 minutes to precipitate the δ phase at the grain boundaries; a second step held at a temperature higher than the temperature of the first step allowing partial dissolution of the δ phase obtained at the first step; ageing treatment comprising a third step and optionally one or more additional steps at a temperature below the temperature of the first step and allowing precipitation of the hardening phases γ′ and γ″. Part thus obtained.