Process for manufacturing a reinforced alloy comprising a metallic matrix, dispersed in the volume of which are nanoparticles, at least 80% of which have a mean size from 1 nm to 50 nm, the nanoparticles comprising at least one nitride chosen from the nitrides of at least one metallic element M belonging to the group consisting of Ti, Zr, Hf and Ta. The process comprises the following successive steps: a) plasma nitriding of a base alloy is carried out at a temperature from 200° C. to 700° C. in order to insert interstitial nitrogen therein, the base alloy incorporating 0.1% to 1% by weight of the metallic element M and being chosen from an austenitic, ferritic, ferritic-martensitic or nickel-based alloy; b) the interstitial nitrogen is diffused within the base alloy at a temperature of 350° C. to 650° C.; and c) the nitride is precipitated at a temperature from 600° C. to 900° C. over a duration of 10 minutes to 10 hours, in order to form the nanoparticles dispersed in the reinforced alloy.