Effects of grain boundary misorientation on solute segregation in thermally sensitized and proton-irradiated 304 stainless steel

The purpose of this study is to investigate the effects of the grain boundary misorientation on the radiation-induced segregation (RIS) in 304 stainless steels. There were four test conditions for the specimens: (1) as-received (AR) with enriched Cr at grain boundary, (2) AR + 1 dpa proton irradiation at 450°C, (3) thermally sensitized (SEN), and (4) SEN + 1 dpa proton irradiation at 450°C. The Cr/Ni-concentration profiles were measured by using FEGTEM/EDS and the grain boundary misorientation was determined with the aid of simulated Kikuchi patterns. A delayed Cr depletion compared to no pre-enrichment condition was found at grain boundaries in AR + 1 dpa specimens. The Cr-concentration profile gets narrower and deeper in SEN + 1 dpa specimens. The degree of grain boundary segregation was observed to be higher at random boundaries than special boundaries. The segregation cusps were measured at grain boundaries of Σ3,Σ9 and Σ15 in SEN + 1 dpa 304 stainless steel specimens. From the fitted segregation cusps, it seems that the Cr segregation level at special boundaries in irradiated sensitized 304 stainless steels increases with Σ for values up to Σ=15.