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工業プロセスで生じる硫酸及びHI流体環境下における耐食性向上を目指したオーステナイト系Fe基合金及びNi基合金の開発方針

Development plan of austenitic Fe and Ni based alloys with improved corrosion resistance to sulfuric acid and HI fluids of industrial processes

広田 憲亮; 岩月 仁; 今井 良行; Yan, X.

Hirota, Noriaki; Iwatsuki, Jin; Imai, Yoshiyuki; Yan, X.

本研究では、オーステナイト系Fe基合金およびNi基合金を、熱化学水素製造プロセス及び地熱発電プロセス等を含む様々な工業プロセスで存在する硫酸及びヨウ化水素を扱う環境での実用構造材料の候補材を開発する。本研究の目的は、これらのプロセス環境下で十分な耐食性能を達成するとともに、セラミックスの製造上のサイズ制限により、現在検討されている材料(SiC)のスケールアップが困難となっていることに対する克服である。オーステナイト系Fe基合金の化学成分開発方針は、Cu, Ta添加によるマトリックス強化、Si, Ti添加による表面被覆強化、希土類元素添加による表面酸化物の剥離の防止である。特にCu, Siの添加は、材料の靭性を低下させ、構造物の加工性を低下させることがわかっているため、各添加元素の許容量を見極めることが重要である。一方、Ni基合金の化学成分開発方針は、Mo, W, Ta添加によるマトリックス強化、Ti添加による表面被覆強化、希土類添加による表面酸化物の剥離の防止である。特にNi基合金へのMo, W添加は、各種プロセス機器の加熱冷却時に生じる構造物の寸法逸脱防止に効果がある。今後は、上記の化学成分開発方針に基づいて様々な材料試験片を作製し、これら試験片を用いた試験として、各工業プロセスを模擬した流体環境下での耐食性能評価を行う予定である。

In this study, austenitic Fe-based alloys and Ni based alloys was developed as candidate structural materials for equipment operated in sulfuric acid and hydrogen iodide (HI) environment, which exists in various industrial processes including iodine-sulfur (IS) hydrogen production process and geothermal power generation process. The objectives of the study are to achieve the corrosion resistance performance sufficient under the working condition of these processes and to overcome the practical scale-up difficulty of the ceramic (SiC) material that is presently used in the processes due to the manufacturing size limitation of the ceramic. The chemical composition development plan for the austenitic Fe-based alloys is threefold: reinforcement of matrix by addition of Cu and Ta, strength compensation of the surface film by addition of Si and Ti, and prevention of peeling of surface oxide by addition of rare earth elements. Because addition of Cu and Si is known to reduce the ductility of the material and thus manufacturability of the component, it is important to determine the allowable amount of each element to be added. On the other hand, the chemical composition development plan for the Ni based alloys is reinforcement of matrix by addition of Mo, W and Ta, strength compensation of the surface film by addition of Ti, and prevention of peeling of surface oxide by addition of rare earth elements. In particular, the addition of Mo and W to the Ni based alloy is expected to be effective in preventing dimensional deviation of structures from increasing during heating and cooling of process equipment. Various material specimens will be fabricated based on the above chemical composition development plans and tests on these specimens will then be carried out to confirm the corrosion resistance performance under the fluid conditions simulating each industrial processes.

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