TEM (transmission electron microscopy), APFIM (atom-probe field ion microscopy), and SANS (small-angle neutron scattering) examination of aged duplex stainless steel components from some decommissioned reactors

The present investigation indicates that the primary embrittlement processes of the CF-8 grade cast stainless steel components during extended reactor service are spinodal decomposition of the ferrite phase and M/sub 23/C/sub 6/ carbide precipitation on the austenite-ferrite boundaries. The ferrite hardness measured for the Shippingport reactor valves appears to reflect the different extent of spinodal decomposition among the different valves which contain slightly different Cr contents. G-phase precipitation was minimal compared to that during accelerated aging of CF-8 steel in the laboratory (i.e., near 400/degree/C). This indicates that the activation energy may be strongly influenced by the synergism among the G-phase precipitation, carbide formation, and spinodal decomposition. 13 refs., 2 figs