Numerical modelling for intergranular corrosion of stainless steel based on microscopic analysis of corroded texture

ステンレス鋼の腐食形態の詳細解析に基づいた粒界腐食過程の数値モデル化検討

山本 正弘 ; 五十嵐 誉廣  ; 小松 篤史 ; 本岡 隆文; 上野 文義  

Yamamoto, Masahiro; Igarashi, Takahiro; Komatsu, Atsushi; Motooka, Takafumi; Ueno, Fumiyoshi

粒界腐食を起こさないEHP合金に不純物元素であるPを添加し、さらに粒界析出を加速する熱処理を行い、粒界部でのPの析出状態を変化させたサンプルの粒界腐食形態を詳細解析した。さらに、その腐食形態をセルオートマトン法を用いてシミュレーションする方法について検討した。その結果、粒界部でのPの析出状態は均一ではなく、その不均一性を考慮した今回のシミュレーション結果は実際の状態を非常によく再現することがわかった。

Intergranular corrosion occurred in stainless steels in nitric acid solution at a spent fuel reprocessing plant. Several reports introduced that intergranular corrosion affected by the impurity elements. We analyzed the initial stages of intergranular corrosion microscopically and attempted to simulate them numerically. The specially prepared 25Cr-20Ni stainless steel which was include only phosphorus for an impurity element was used for analyzing the initial stage of intergranular corrosion. Phosphorus segregated into grain boundary using various thermal treatments. The results indicated that the initial stage of intergranular corrosion was characterized by the ratio of corrosion rates between grain boundary and matrix. The ratio increased with higher phosphorus segregation by thermal treatment. These values were used for numerical simulation of intergranular corrosion. The cross sectional images calculated by the simulation were very good agreement to the actual observations.