鐵錳鋁合金鋼又稱為錳鋁鋼，是學術界研發中的不銹鋼，其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銹鋼的潛力。錳鋁鋼相變化的研究是提供錳鋁系不銹鋼發展的必要基礎。本論文即為研究鐵-19.6錳-7.7鋁-0.28碳(wt.%)合金鋼經不同熱處理後的相變化情形；熱處理包括：1300℃、1200℃和1100℃的高溫熱處理與1100℃固溶處理後的低溫恆溫處理。本合金鋼於1300℃以下溫度的金相組織為肥粒體(α)與沃斯田體(γ)共同組成的雙相結構。合金鋼經1200℃以上溫度以水淬急速冷卻，於雙相的肥粒體晶粒內有針狀18R麻田散體的生成。若先經1100℃固溶處理再於700℃以下溫度做恆溫處理，則肥粒體晶粒內有析出物的出現。本合金鋼於1100℃時以水淬、空冷與爐冷的方式冷卻，則於肥粒體晶粒內發生有序化相變化，其反應式為 α → α + D03，其中細小顆粒狀的有序D03超晶格相均勻的分佈於肥粒體晶粒內。本論文主要是探討合金鋼內 α → α + D03有序化相變化，且判定D03相的生成上限溫度是介於460℃至435℃之間。

The low-density and low-cost Fe-C-Mn-Al steels have been studied for decades. One of the most important objects for the development of the Fe-C-Mn-Al steels is to replace some of the Ni-Cr stainless steels. Phase transformations are the basic requirement for the development of the Fe-C-Mn-Al steels. We have studied the phase transformations of the Mn-Al steels for more than 20 years. The object of the thesis is to investigate the phase transformations of an Fe-0.28 C-19.6 Mn-7.7 Al steel after various heat treatments including high-temperature heat treatments at 1300℃, 1200℃ and 1100℃, and low-temperature isothermal holding at temperatures below 800℃ after solution treatment at 1100℃. The steel is composed of dual phases of ferrite (α) and austenite (γ). Upon quenching the steel samples from temperatures above 1200℃, needle-like 18R martensite appears in the ferrite grains of the dual structure. Second phase precipitates in the ferrite grains upon isothermal holding at temperatures below 700℃. Fine D03 particles appear in the ferrite grains according to an ordering reaction, α → α + D03, occurs in the ferrite grains after heating the steel at and cooling, either quenching, air-cooling, or furnace-cooling, from 1100℃. The upper temperature limit for the appearance of the D03 phase is between 460℃ and 435℃.

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