Abstract
Long-term stress relaxation behavior was investigated on NCF 800H alloy. Complicated stress relaxation behaviors such as rapid decrease of residual stress and increase of residual stress were observed. Relationship between stress relaxation behavior and microstructural changes was examined. The decrease of residual stress was caused by the reduction of creep deformation resistance due to coarsening of carbides. Minus relaxation behavior which is equivalent to the increase of residual stress was related to shrinking of testing material due to precipitation of carbides. Therefore, it is difficult to extrapolate the long-term stress relaxation curve from the result of short-term tests, and the long-term residual stress value should be predicted using aged material.
