LONG TERM THERMAL AGING OF TYPE CF 8 STAINLESS STEEL

Atom Probe Field-Ion Microscopy and Transmission Electron Microscopy have been used to characterize the microstructure and to determine the changes that occur during long-term low-temperature aging of primary coolant pipes used in pressurized water nuclear reactors. The cast CF 8 type stainless steel forms a mixture of austenite and ferrite. On aging 10 nm diameter precipitates, tentatively identified as G-phase, formed in the ferrite. The ferrite matrix also decomposed into a fine scale mixture of a chromium-enriched phase and an iron-rich phase similar to the transformation products in iron-chromium-X systems that spinodally decompose.