錳鋁合金鋼具有取代鎳鉻系不銹鋼的潛力，而錳鋁鋼相變化研究則是提供發展錳鋁不銹鋼的重要基礎。本論文是研究成份為鐵-6.3錳-7.9鋁-0.14碳(wt.%)錳鋁合金鋼的高溫相變化。實驗方法為加熱錳鋁鋼至1300℃至1100℃溫度區間後，以水淬或空冷方式冷卻至室溫。經分析後確認本錳鋁鋼於1200℃以上溫度為單相的肥粒體，而於1100℃為肥粒體與少量沃斯田體的雙相組織。我們發現經高溫空冷方式冷卻的肥粒體晶粒內析出大量的沃斯田體魏德曼組織，而於魏德曼晶粒內存在著細小顆粒狀的L12相。推判此類魏德曼沃斯田體晶粒發生spinodal相分離與有序化相變化。總結如下：於空冷過程的高溫區，肥粒體基地(α)會先行生成沃斯田體魏德曼組織(Widγ)；而後於冷卻過程的低溫區，此沃斯田體魏德曼晶粒內發生spinodal相分離與有序化相變化，使高溫沃斯田體魏德曼組織(γ)於較低溫時經spinodal相分離而分離成低溫無碳沃斯田體(γ’)與富碳沃斯田體(γ”)，其反應式如下：γ→γ’+γ”；經spinodal相分離後的合金鋼冷卻至更低溫時，富碳之γ”相會經由有序化相變化而轉變為富碳之L12相，反應式為γ” →L12。以上的總反應式為：α→α+Wid(γ’+L12)。

Mn-Al steels have the potential to substitute some commercial Ni-Cr stainless steels. For the development of Mn-Al stainless steels, phase transformations play an important role for the provision of the basic knowledge of the steels. The methodology of studying the phase transformations of the Fe-6.3 Mn-7.9 Al-0.14 C (wt.%) steel includes heating the steel samples to high temperatures ranging from 1300℃ to 1100℃ and air-cooling to room temperature. The steel is single ferrite (α) at temperature above 1200℃, and is dual phase of ferrite and austenite at 1100℃. Lots of Widmanstatten austenite grains appear in the ferrite matrix after air cooling from high temperature. We have also found the Widmanstatten austenite grain is composed of austenite and fine L12 particles via the observation in a transmission electron microscope. We have found the occurrence of the spinodal decomposition and ordering reaction in the Widmanstatten austenite after air cooling from high temperature. At the high temperature stage of air cooling, austenite has undergone the spinodal decomposition and decomposes into two other low temperature austenite phases. One is carbon-lean austenite (γ’), and the other is carbon-enriched austenite (γ”). The spinodal decomposition is shown as follows. γ→γ’+γ”. Upon further cooling, the carbon-enriched austenite has undergone the ordering reaction and becomes the L12 phase, i.e. γ” →L12. The overall reactions occur in the high temperature ferrite is as follows. α→α+Widγ→α+Wid(γ’+γ”) →α+Wid(γ’+L12).

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