In this study,tensile behavior of Nb-containing 25Cr-20Ni austenitic stainless steels composed of coarse or fine grains has been investigated at temperatures ranging from room temperature to 900 ℃.Results show that the tensile strength of fine-grained specimens decreases faster than that of coarse-grained specimens,as the test temperature increases from 600 ℃ to 800 ℃.The rapidly decreasing tensile strength is attributed to the enhanced dynamic recovery and recrystallization,because additional slip systems are activated,and cross-slipping is accelerated during deformation in fine-grained specimens.After tensile testing at 700-900 ℃,sigma phases are formed concurrently with dynamic recrystallization in fine-grained specimens.The precipitation of sigma phases is induced by simultaneous recrystallization as the diffusion of alloying elements is accelerated during the recrystallization process.Additionally,the minimum ductility is observed in coarse-grained specimens at 800 ℃,which is caused by the formation of M23C6 precipitates at the grain boundaries.