Long term stress relaxation properties of NCF 800H alloy
Ohba Toshio; Kanemaru Osamu; Yagi Koichi; Tanaka Chiaki
Abstract:Long term stress relaxation behavior was investigated on NCF 800H alloy. Complicated stress relaxation curves such as those with rapid decrease or increase in residual stress were observed. Their relationship between stress relaxation behavior and microstructural change was examined. The rapid decrease in residual stress was caused by the reduction of creep deformation resistance due to coarsening of carbides. Minus relaxation behavior which expresses the increase in residual stress was related to the 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 stress relaxation value should be predicted using the aged material. Key Words:NCF800H alloy, stress relaxation, microstructural change, minus relaxation behavior