Dissolution temperature of Ni-Si-Mn precipitates in steels; When they became compounds

松川 義孝*; 藤枝 秀斗*; 牟田 浩明*; 中森 文博*; 山口 正剛   ; 笠田 竜太*; 吉田 健太*; 藪内 聖皓*; 遠藤 美奈子*; 熊野 秀樹*

Matsukawa, Yoshitaka*; Fujieda, Hideto*; Muta, Hiroaki*; Nakamori, Fumihiro*; Yamaguchi, Masatake; Kasada, Ryuta*; Yoshida, Kenta*; Yabuuchi, Kiyohiro*; Endo, Minako*; Yuya, Hideki*

The dissolution temperatures of irradiation-induced Ni-Mn-Si precipitates in reactor pressure vessel steels were investigated using so-called diffusion couples consisting of compound ingots and iron blocks to provide a detailed analysis of atomic diffusion across the precipitate/matrix interface. The dissolution temperature of phase G NiSiMn was found to occur even at 565C, unlike NiSiTi with different compositions examined in previous studies. The 2 phase, a possible Ni-Si-Mn compound (NiSiMn) with a composition of over 60 years, was also found not to dissolve at 565C. The accuracy of the Thermocalc simulations is still not satisfactory in describing the melting point and chemical diffusion (a thermodynamic mode of atomic diffusion, related to precipitation and dissolution) of the Ni-Si-Mn-Fe system.