Abstract: A detailed knowledge of changes in microstructures and mechanical properties that occur in AISI 321 stainless steels service before and after solution treatment is of great interest, since the ductility and toughness of AISI 321 stainless steels may change drastically after service for a long time. After solution treatment at 1050 ℃, the microstructures of AISI 321 stainless steels service for 80 000 h at 700℃ indicate that the content of sigma phase significantly decreased, the grains of austenite grew and the amount of twins together with the size increased with solution treatment time. The results of mechanical properties tests show that the impact toughness at room temperature was superior at solution treatment, and there was no obvious change in the impact toughness between different times of solution treatment at room temperature.

Key words: Austenitic stainless steels, Microstructure, Mechanical properties, Solution treatment, Sigma phase