鐵錳鋁合金鋼又稱為錳鋁鋼，具有低密度與低原料成本的優勢，且有取代部份傳統鎳鉻系不鏽鋼的潛力。錳鋁鋼相變化的研究是提供錳鋁系不鏽鋼發展的必要資訊基礎。本論文研究鐵-19.6錳-7.7鋁-0.28碳(wt.%)合金鋼的相變化。錳鋁鋼經1100℃熱處理後，不論以水淬或是空冷方式冷卻，於肥粒體晶粒內皆觀察到均勻析出的D03顆粒。推測發生spinodal相分離與有序化反應。經由TEM高解析晶格影像分析，可區分出清楚與模糊區域的晶格影像，推論可能是對應碳原子的分離，其以快速的間隙型擴散產生貧碳與富碳的肥粒體區域，當富碳肥粒體未能持續完成後續的有序化反應以形成D03相，則導致於富碳肥粒體區域的部份晶格扭曲，所對應的是模糊TEM晶格影像區域。於TEM-EDX的成分分析發現碳元素確有明顯的差異現象，這亦可以推測是經由spinodal相分離所形成。合金鋼於750℃以下溫度，於肥粒體晶粒內觀察到析出物的出現。溫度為700℃至600℃時，析出物是魏德曼沃斯田體；當溫度低於600℃時，則觀察到碳化物。

The low-density and low-cost Fe-C-Mn-Al steels have been studied for decades. Phase transformations are the basic requirement for the development of the Fe-C-Mn-Al steels. We have found that Fe-19.6Mn-7.7Al-0.28C (wt.%) alloy steel has undergone the ordering reaction to form D03 phase after heating at 1100℃ and cooling with either quenching or air cooling. We believe the steel has undergone the spinodal decomposition which high temperature ferrite has decomposed into two other low temperature ferrites both with carbon-lean and carbon-enriched contents, and ordering reaction which carbon-enriched ferrite has transformed into D03. Through the high-resolution TEM study, we have observed lattice point fuzzy area from the lattice distortion due to the high carbon content. In AEM analysis, the distribution of the carbon concentration deviation presumably shows that the spinodal decomposition occurs. Second phase precipitates in the ferrite grains upon isothermal holding at temperatures below 700℃. At temperatures between 700℃ and 600℃, Widmanstatten austenite forms in the ferrite grains. When the aging temperature is lower than 600℃, -carbide forms in the ferrite grains.

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