熱浸鋁塗層於氯化鈉熱腐蝕之防制作用

The Performance of Hot-dipped Aluminum Coating on the Corrosion Resistance in NaCl-Induced Hot Corrosion

本研究選用低碳鋼、310不銹鋼及鐵錳鋁鉻矽碳三式合金、於700℃實施10秒之熱浸純鋁，並以熱浸鋁以及熱浸鋁後在900℃預氧化2小時之表面狀態，於900℃靜態空氣氣氛進行1～144小時9mg/cm2氯化鈉之沉積熱腐蝕試驗。藉由金相觀察、侵蝕深度、熱重動力學資料、EPMA定性與定量分析等方式，探討鋁塗層及其預氧化處理對三式合金熱腐蝕特性之改善作用。實驗結果顯示，低碳鋼及310不銹鋼熱浸鋁處理後，不但於反應初期有效阻隔氯化鈉之侵蝕，而且經由合金化層的生成，提供合金氧化鋁自我修護之能力，使抗讓腐蝕特性明顯提昇。然而，鐵錳鋁鉻矽碳合金由於對鋁具有高度的固溶度，鋁塗層於熱腐蝕時快速擴散進入合金，除誘發複雜的相變化外，合金表層亦發生嚴重的氮侵蝕反應，氮化鋁之生成反而降低了合金原有之抗熱腐蝕特性。熱浸鋁後之預氧化處理促進合金化層之成長，於冷卻時產生的表層微裂縫，提供了液態氯化鈉積存的位置及滲入途徑，使得其腐蝕速率較未經預氧化試片為高。

In order to understand the NaCl hot corrosion behavior of materials in static air at 900℃. Low carbon steel, 310 stainless steel and Fe-Mn-Al-C alloy were applied in this study, including its hot-dipped aluminum (700℃ /10sec.) and preoxidation (900℃/2hr in air) surface treatments. More then made a full realization about the improvement of corrosion resistance to NaCl hot corrosion by aluminum was applied. The corrosion resistance of Fe-Mn-Al-C alloy to chlorine was better than low carbon steel and 310 stainless steel, because of the protective Al2O3 scale was formed. After hot-dipped aluminum treatment, 310 stainless steel had excellent performance by the formation of Al2O3 scale, the weight gain and long-term corrosion resistance were better than low carbon steel which hot-dipped aluminum. However, due to the high aluminum solubility in Fe-Mn-Al-C alloy, the dipped aluminum dissolved into Fe-Mn-Al-C alloy at high temperature. The higher aluminum content in alloy substrate induced nitrogen attack. At the same time, the formation of AlN depleted the aluminum. As a result, the corrosion resistance of alloy was loss. Preoxidation of these materials not only created lots of microcracks which became the penetrating path of molten NaCl salt and chlorine, but also enhanced the growth of alloying layer and diffusion of aluminum in metal. There were much imperfection in long-term corrosion resistance.