Mechanical properties and microstructure changes have been investigated on a new nickel-base superalloy after long-term aging at 700℃ It is found that the major precipitates of the tested alloy are MC, M23C6, M6C and in the course of long-term aging at 700℃. The carbides maintain good thermal stability with the aging time up to 5008 h. The growth rate of gamma prime precipitates is relatively high in the early aging period and then slows down. The coarsening behavior of gamma prime follows a diffusion-controlled growth procedure. The room temperature Rockwell hardness of the alloy aged at 700C increases slightly at the initial stage of aging, but it decreases with the prolonged time. It mainly depends on the size of gamma prime. In comparison with Nimonic Mechanical properties and microstructure changes have been investigated on a new nickel-base superalloy after long-term aging at 700 ° C. It is found that the major precipitates of the tested alloys are MC, M23C6, M6C and in the course of long-term aging at 700 ° C. The carbides maintain good thermal stability with the aging time up to 5008 h. The growth rate of gamma prime precipitates is relatively high in the early aging period and then slows down. The coarsening behavior of gamma prime follows a diffusion-controlled growth procedure. The room temperature Rockwell hardness of the alloy aged at 700C increases slightly at the initial stage of aging, but it decreases with the prolonged time. It mainly depends on the size of gamma prime. In comparison with Nimonic