Abstract. To understand the role of different metallurgical parameters on the void formation mechanisms, various austenitic stainless steels were elaborated and irradiated with heavy ions. Two alloys, in several metallurgical conditions (15Cr/15Ni-Ti and 15Cr/25Ni-Ti), were irradiated in the JANNUS-Saclay facility at 600°C with 2 MeV Fe 2+ ions up to 150 dpa. Resulting microstructures were observed by Transmission Electron Microscopy (TEM). Different effects on void swelling are highlighted. Only the pre-aged samples, which were consequently solute and especially titanium depleted, show cavities. The nickel-enriched matrix shows more voids with a smaller size. Finally, the presence of nano-precipitates combined with a dense dislocation network decreases strongly the number of cavities.