Ion irradiation effect on micro structures of heat affected zone under stainless overlay clad in RPV steel

Ha, Yoosung  ; Takamizawa, Hisashi ; Hanawa, Satoshi ; Nishiyama, Yutaka ; Ebisawa, Naoki*; Yoshida, Kenta*; Toyama, Takeshi*; Nagai, Yasuyoshi*

Stainless overlay clad is welded on the inner surface of the reactor pressure vessel steel to prevent corrosion by the primary coolant. Heat affected zone (HAZ) is created during the welding and the micro structure at the HAZ is different from that of the base metal. This microstructural difference would cause the difference in irradiation hardening as well as embrittlement between the HAZ and the base metal. In order to confirm the irradiation embrittlement susceptibility of HAZ, Fe2+ ion irradiation experiment was carried out to both the HAZ and the base metal in this study. As results of TEM observation, precipitates dispersed with the size of ~200 nm in SCFGHAZ. Also, finer and higher number density of solute clusters were observed in the HAZ than that of the base metal by the atom prove tomography analysis. It was considered that the higher irradiation hardening of HAZ was caused by the precipitates and these solute clusters.