近年來雙相不銹鋼作為功能型材料被廣泛應用在海水處理廠、石化工業等產業，其中應用最為廣泛是2205雙相不銹鋼。許多研究中顯示2205雙相不銹鋼於水溶液中會產生選擇性腐蝕，對2205雙相不銹鋼的高溫氧化也有提出可能之相變化機制，但現有的文獻並未對雙相不鏽鋼於高溫環境中是否也會產生選擇性腐蝕及表面氧化物在不同氧化溫度與時間下的變化進行深入討論。另外雙相不鏽鋼常使用在含碳氣體的環境下，因此本實驗將2205雙相不銹鋼於700-900 °C的空氣中及碳勢氣氛下分別進行2-96小時的暴露試驗，利用掃描式電子顯微鏡、能量散色光譜儀與X光繞射儀對表面腐蝕產物進行分析，並使用掃描式電子顯微鏡觀察基材內微觀組織相變化。結果顯示，試驗後空氣中與碳勢氣氛下的表面腐蝕產物的組成成分相似，但形貌差異大，於空氣中隨氧化溫度提高，氧化物顆粒的優選取向變明顯，並且隨著氧化時間增加，氧化顆粒粗大化；於碳勢氣氛下，暴露溫度700、800 °C時，表面腐蝕產物的粒徑較小且優選取向不明顯，當暴露溫度達900 °C時有部分腐蝕產物的氧化速率較快，形成長柱狀腐蝕產物。在空氣與碳勢下高溫暴露後，於α相上方的銹皮皆略厚於γ相上方之銹皮。於高溫試驗後，基材析出富鉻的σ相與富鉬的χ相，γ、σ相隨氧化時間增加體積百分率上升，χ、α相則隨氧化時間增加體積百分率降低；在碳勢氣氛下，各相體積百分率變化趨勢與空氣中相似，但σ相在氧化24小時後增率放緩，另外，靠近銹皮下方之基材γ相的增加幅度相較空氣環境中的試片大，顯示了碳原子的滲入對γ相的穩定作用。

The purpose of this study is to explore the phase transformation and high temperature oxidation behavior of 2205 duplex stainless steel in a high carbon activity atmosphere. Carbon activity was controlled by CO/CO2 mixed gas. The corrosion product morphologies and structure were analyzed by the scanning electron microscope (SEM) and X-ray diffractometer (XRD), respectively. The phase identification was evaluated by the image contrast of backscattering electron (BSE) images and energy dispersive spectroscope (EDS). The experimental results showed the element composition and structure of corrosion products in the air and carbon activity atmosphere are similar, while the morphologies were different. Oxidation in the air, as the temperature increased, the corrosion product was coarse. When the temperature reached 900 °C, a part of the corrosion product formed the column crystal. After the high temperature test, the chromium-rich σ phase and the molybdenum-rich χ phase were precipitated. The volume fraction of the γ and σ phases increased with the increase of the oxidation time, and the volume fraction of the χ and α phases decreased with the increase of the oxidation time. The changing trend of the volume fraction of each phase is similar to that in the air, but the growth rate of the σ phase slowed down after 24 hours. In addition, the volume fraction of the γ phase in the carbon activity atmosphere increased larger than the sample in the air. It showed that the carbon atoms could stabilize the γ phase.

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