The Effect of Phosphorus on the Radiation-Induced Microstructure of Stabilized Austenitic Stainless Steels

This paper deals with the correlation of irradiation behavior and microstructural evolution of mono-(Ti) and multi-(Ti, Mb, V) stabilized Type 316 (UNS S31600) stainless steels with different phosphorus levels. These steels, in the 20% cold-worked condition, were irradiated between 400 and 500°C up to 100 dpa in the Phenix reactor as stressed and unstressed samples. Phosphorus strongly decreases the swelling of stabilized austenitic steels. This effect is due to a large increase of the swelling incubation dose. The best swelling resistance is observed for the multistabilized (Nb, V, Ti) steel. Phosphorus also decreases the irradiation creep strain, but only because of the decrease in swelling. The transmission electron microscopy (TEM) examinations show that the improvement of swelling resistance by phosphorus addition comes from a decrease in void density, which occurs mainly when a uniform distribution of needle-shaped phosphides appears. In titanium-stabilized steels, the phosphides are FeTiP, whereas in the phosphides of the multistabilized steel, titanium is replaced by niobium, leaving the titanium in solution to play its role as a swelling inhibitor for long-term irradiations.