The effect of residual δ-ferrite (～2%) on the stresscorrosion cracking (SCC) behavior of 321 stainless steel(SS) base metal from a dissimilar weld joint wasinvestigated by direct current potential drop (DCPD)method with an “on the fly” change of water chemistry insimulated light water reactor (LWR) water environment.The results show that 321SS is a highly SCC resistantmaterial. The improved SCC crack growth rate (CGR)performance, from 3.3×10~(-8) mm/s to 1.6 ×10~(-9) mm/s, andthe absence of a Cl- acceleration effect on CGR werecaused by the dispersed island-shape δ-ferrite. The SCCresistant δ-ferrite inhibited the growth of cracks andforced the crack to propagate along the phase boundary,where neither elevated residual strain nor significant Crdepletion could be found. The dispersed island-shape δ-ferrite works as a Cr source to facilitate the less solubleCr-rich oxides formation at phase boundaries.Furthermore, the dispersed Ti(CN)x particles at the γ/δphase boundaries in Ti-modified austenitic 321SS tends toblunt the crack tip, inhibits phase boundary oxidation,and facilitates the less soluble Cr/Ti rich oxides formation,thus impeding the SCC growth when the crack was forcedto propagate along the γ/δ phase boundary.
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