At intermediate temperatures where SIAs and vacan­cies are mobile, significant solute segregation to point defect sinks can occur. This can lead to precipitation of new phases due to the local enrichment or deple­tion of solute. These radiation-induced or — enhanced precipitation reactions typically become predominant

phenomena in irradiated ferritic and austenitic steels at elevated temperatures for doses above about 10 dpa, and in irradiated reactor

pressure vessel steels at low dose rates for damage levels above 0.001-0.01 dpa.247,248 Some general aspects of radiation-induced and — enhanced solute segregation and precipitation were described previ­ously in Section 1.03.3.9. The solute segregation and precipitation associated with irradiation can lead to several deleterious effects including property degradation due to grain boundary or matrix embrit-

tlement224,247,249-252 and enhanced susceptibility for localized corrosion or stress corrosion cracking.253-256 Solute segregation and precipitation can lead to either enhanced or suppressed void swelling

behavior.149,257,258 For austenitic stainless steel,

undesirable precipitate phases that generally are associated with high void swelling include the radiation-induced phases M6Ni16Si7 (G), Ni3Si (g0), MP, M2P, and M3P, and the radiation-modified phases M6C, Laves, and M2P200 The undesirable radiation-induced and — modified phases generally are associated with undersized misfits with the lattice, which tends to preferentially attract SIAs and thereby enhance the interstitial bias effect. Figure 26 shows an example of enlarged cavity formation in association with G phase precipitates in neutron- irradiated austenitic stainless steel.106 Potentially desirable radiation-enhanced and — modified phases (when present in the form of finely dispersed precipi­tates) include M6C, Laves, M23C6, MC, s, and w200