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松川 義孝*; 藤枝 秀斗*; 寺尾 公志*; 連川 貞弘*; 牟田 浩明*; 中森 文博*; 笠田 竜太*; 吉田 健太*; 佐藤 充孝*; 藪内 聖皓*; et al.
no journal, ,
圧力容器鋼の脆化要因であるNi-Si-Mn三元系化合物およびFeを加えた四元系化合物について、Thermo-calcを用いて計算状態図を作成した。一方、三元系化合物の単相インゴットと純鉄インゴットの組み合わせから析出物と母相の界面を模擬した拡散対を作成し、拡散挙動について調査し、その振る舞いと状態図との整合性を調査した。その結果、計算状態図におけるいくつかの問題点が明らかとなった。
相Ni
SiMn
の再固溶温度の調査藤枝 秀斗*; 松川 義孝*; 連川 貞弘*; 渡邊 大樹*; 牟田 浩明*; 山口 正剛; 笠田 竜太*; 吉田 健太*; 佐藤 充孝*; 藪内 聖皓*; et al.
no journal, ,
圧力容器鋼の脆化要因であるNi-Si-Mn三元系化合物のG相Ni
Si
Mn
と
2相Ni
SiMn
について、単相インゴットと純鉄のインゴットとの界面を模擬した拡散対を作り、アニール実験を行った。その結果、相における相互拡散の臨界温度はG相よりも高く、低温では拡散が起こりにくいが、高温になると逆に拡散しやすくなることが分かった。
2-phase; C15 Laves phase in RPV steel松川 義孝*; 藤枝 秀斗*; 連川 貞弘*; 牟田 浩明*; 熊野 秀樹*; 笠田 竜太*; 吉田 健太*; 藪内 聖皓*; 山口 正剛
no journal, ,
The 2-phase Ni3SiMn2 is one possible configuration of irradiation-induced Ni-Si-Mn precipitates (a.k.a. the late blooming phase) in the rector pressure vessel (RPV) steel of light water reactors. Unlike the other possible configurations such as the G-phase NiSiMn, this intermetallic compound is crystallographically characterized as the C15 Laves phase, which is of particular interest in fundamental irradiation damage study, specifically in relation to nucleation of interstitial-type dislocation loops. Although the dislocation loop is a planar, 2D cluster, recent simulation studies have suggested that its nucleus is not 2D but 3D, crystallographucally identical to the C15 Laves phase. Hence in the modeling of microstructure evolution in the RPV steel the relation between the 2-phase and the dislocation loop may be a key harnessing irradiation-induced precipitation and dislocation loop formation. We have recently succeeded in fabricating ingots of the 2-phase by means of arc melting, and examined the validity of existing Ni-Si-Mn phase diagrams. It appears that both experimental (Kuz'ma 1964) and simulation (Thermocalc TCNI12) diagrams are not valid.
松川 義孝*; Terao, Masayuki*; 藤枝 秀斗*; 連川 貞弘*; 牟田 浩明*; 熊野 秀樹*; 笠田 竜太*; 吉田 健太*; 藪内 聖皓*; 中森 文博*; et al.
no journal, ,
The primary cause of irradiation-induced embrittlement of the reactor pressure vessel (RPV) steel is precipitation of its alloying elements (Ni, Si and Mn) in the form of nano particles (2 nm). The RPV embrittlement practically limits the service life of the whole reactor; in other words, reactor's lifetime prediction is achieved by predicting the precipitation. Although precipitation under irradiation is a thermodynamically non-equilibrium reaction, recent studies have revealed that precipitation of those elements does occur even without irradiation. Hence the phase diagram of Ni-Si-Mn precipitates in steels has become a subject of interest in nuclear materials research. In this talk we demonstrate that the calculation phase diagram is still incomplete due to absence of experimental data about Ni-Si-Mn ternary compounds; there exist 10 in the phase diagram. We synthesized an ingot of the G-phase NiSiMn, which is one of the most frequently observed precipitates in the RPV steel, by arc-melting and examined the melting point and the composition range. The experimentally-determined melting point was inconsistent with simulation results, e.g., an old database (2016 version) resulted in an overestimation greater than 700 degree of Celsius. As for composition range, although off-stoichiometry is not considered in the calculation phase diagram, the G-phase certainly has it. The same thing happens to the 2-phase NiSiMn, which is another most frequently observed precipitates in the RPV steel.
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*
no journal, ,
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 565
C, 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.