鐵鉻鎳合金於熔融氯化鈉之高溫腐蝕

High-temperature Corrosion of Fe-Cr-Ni Alloys in Molten NaCl

本研究使用三種商用鐵鉻鎳合金（310SS、253MA、353MA）於850℃之氯化鈉熔鹽進行高溫腐蝕，探討合金高溫熔鹽腐蝕之反應機制以及合金元素對腐蝕形態之影響。實驗結果顯示，高溫腐蝕過程經歷兩階段：第一階段為包括氧化皮膜的初始生成及氯化反應所造成皮膜的破壞；第二階段為因皮膜破裂、剝落而產生的電化學腐蝕反應。合金在浸泡於熔融氯化鈉之低氧高氯腐蝕環境中，氯化及電化學反應造成合金的損耗，並於合金表面產生孔洞，其數量隨鉻含量的提升而增加。經長時間的作用，孔洞會相互連結而產生片狀的脫落。合金元素中，以鉻具有最大之溶失傾向，因此含鉻量最高之353MA有最大的內侵蝕深度。在鎳、鉻相互作用影響下，310SS具有最小的金屬損失及總侵蝕深度。

Three commercial Fe-Cr-Ni alloys including 310SS, 253MA and 353MA were studied at 850℃ in molten sodium chloride bath to investigate the corrosion mechanism and the effects of alloying elements on the hot corrosion morphology. The results showed that hot corrosion proceeds in two stages: an initial oxychlorination/chlorination, followed by electrochemical reactions. In the initial oxychlorination/chlorination period, oxide scales formed by oxychlorination were broken by chlorination. After the scales broke and peeled off, corrosion attack was dominated by electrochemical reactions. In the molten salt with low oxygen and high chlorine activity, chlorination and electrochemical reactions caused metal loss of the alloys and the occurrence of pitting in the alloy substrate near the alloy substrate-salt interface. The amount of voids increased with increasing chromium content in the alloys. The coalescence of voids resulted in falling off of metal flakes after long-term immersion. In this study, 310SS exhibited better corrosion resistance than 253MA and 353MA.