Acciaio ferritico ODS per il settore nucleare

Oxide dispersion strengthened steels are candidate materials for structural constituents in IV generation fission nuclear reactors and for fusion nuclear reactors. A reduced activation nano-oxide strengthened ferritic steel is produced by mechanical alloying with an average grain size of 400 nm. The steel is produced starting from nanometric powders of Fe-14Cr-1W-0.4Ti mixed with 0.3% Y2O3 powders, grinded by a low-energy mechanical alloying for 300 h and additionally consolidated by hot extrusion. Different heat treatments are carried out in temperature range from 1050 °C and 1150 °C. Transmission electron microscopy (TEM) analysis of hot extruded sample shows a equiaxed ferritic microstructure (Fig. 1a) with a high dislocation density (Fig. 1b) and a massive precipitation of different oxides particles (Fig. 2a) and complex non stoichiometric nano-oxide particles Y-Ti-O lesser than 10 nm (Fig. 2b). The precipitates distribution exhibits a remarkable stability in temperature and reduces the loss of mechanical characteristics even after extended exposure at 800 °C. After the heat treatments at 1050-1150 °C, the microstructure evolves towards a bimodal grain distribution as showed in Fig. 3. An inhomogeneous distribution of oxide particles inside the grains and different particles sizes after the heat treatment are showed respectively in Fig. 4 (a-b) and Fig.5 (a-b).