錳鋁合金鋼是學術界研發中的低密度不鏽鋼，具有取代部分傳統鎳鉻系不鏽鋼的潛力；而相變化的研究則是提供發展錳鋁系不鏽鋼的基礎。本論文研究低碳鐵錳鋁合金鋼內麻田散肥粒體晶粒發生的spinodal相分離與有序化相變化。著重於分析成分為鐵-14.2錳-3.93鋁-0.16碳(wt.%)的A合金鋼相變化，再配合與鐵-16.7錳-3.42鋁的B合金鋼以及鐵-14.3錳-2.91鋁的C合金鋼的相變化做比較。以上三種錳鋁鋼於1100˚C高溫經水淬、空冷及爐冷方式冷卻後皆發生麻田散體相變化，於高溫沃斯田體內可觀察到麻田散肥粒體的生成。且A合金鋼經加熱至1100˚C後冷卻，於麻田散肥粒體內可觀察到均勻的細小D03相顆粒的分佈。而後對水淬A合金進行低溫恆溫處理，亦發現細小D03顆粒分佈於肥粒體內，且在400˚C爐冷的合金內的肥粒體晶粒會形成次晶。經由TEM-EDX的成分分析，發現零碳含量與富碳含量的局部區域，證實肥粒體由高溫冷卻時會相分離形成兩個低碳與富碳肥粒體相，其中富碳肥粒體相於再冷卻過程藉由有序化相變化形成D03相，整體相變化過程為：α → α’+ α’’→ α’+ D03。

Fe-C-Mn-Al steels have the potential to substitute the commercial Ni-Cr stainless steels. For the development of Fe-C-Mn-Al stainless steels, phase transformations play an important role. The phase transformations we studied in the thesis include spinodal decomposition and ordering reaction of the low-carbon Fe-Mn-Al steels. We have focused ourselves on studying the phase transformations of alloy A (Fe-14.2 Mn-3.93 Al-0.16 C), and have compared the results with two other carbon-free alloys which include alloy B with the composition of Fe-16.7 Mn-3.42 Al and alloy C with the composition of Fe-14.3 Mn-2.91 Al. We have observed D03 precipitate according to the spinodal decomposition, which high-temperature ferrite (α) has decomposed into carbon-lean ferrite (α’) and carbon-enriched ferrite (α’’), and ordering reaction which the carbon-enriched ferrite has undergone the ordering reaction and transformed into D03 phase in the martensitic ferrite by TEM. The overall reactions are α → α’+ α’’ → α’+D03.

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