フェーズフィールド法による高温安定性フェライト鋼における窒素吸収・相変態挙動の解析

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タイトル別名
  • Phase Field Simulation Analysis of Nitrogen Absorption-Phase Transformation Behavior in the High Temperature Stable Ferritic Stainless Steel
  • フェーズフィールドホウ ニ ヨル コウオン アンテイセイ フェライトコウ ニ オケル チッソ キュウシュウ ・ ソウヘンタイ キョドウ ノ カイセキ

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The behavior of diffusion and phase transformation in a high temperature stable ferritic stainless steel (SUS444) nitrogen-absorbed at 1450 K for 4 hr under 0.4 MPa N2 gas was investigated with EPMA mapping. While Cr content in the nitrogen absorption layer (NA layer: γ phase) increased, Mo discharged from NA layer was enriched in the grain boundary of α/γ. Using a 1D-phase field simulation (PFS), the phenomenon during the NA treatment in the Fe-19Cr-2Mo-0.5Mn-N alloy was discussed. In the case of PFS with impurity diffusion (lattice diffusion) coefficients in Fe, since the diffusion velocity in γ phase was smaller than that of α phase, concentration distribution between NA layer and matrix α phase is caused by local phase equilibrium in depending on the composition of NA layer. Additionally, diffusion of substitutional atoms is slower than the growing velocity of NA layer that is depended on nitrogen diffusivity. This is the reason why Cr content in the NA layer fluctuates and why the average compositions in α phase and NA layer has the opposite trend with thermodynamic calculated and experimental results. On the other hand, in the case of the simulation under Dγ > Dα in consideration of the grain boundary diffusion of substitutional elements, the segregation behavior of solute elements was in good agreement with the results of EPMA mapping. Thus, it was confirmed that not only the diffusion of N atoms but also the grain boundary diffusion contributes greatly to the growing phenomenon of NA layer in a high stable ferritic stainless steel.

収録刊行物

  • 鉄と鋼

    鉄と鋼 101 (6), 336-342, 2015

    一般社団法人 日本鉄鋼協会

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