In this paper the results of secondary phases determination in a SAF 2205 duplex steel, heat treated at 780, 850 and 900 degrees C for 10-40 min, are presented. chi-phase is the first phase to precipitate at all the temperatures, followed by sigma-phase. The main drop of toughness is related to very low contents of chi-phase and sigma-phase. Hardness is not a sensitive parameter to low amounts of secondary phases.