本論文研究成份為鐵-19.1錳-0.97碳(wt%)之高錳鋼的恆溫相變化情形。高錳鋼的前處理為1100℃的高溫固溶處理，接著於825至500℃的溫度區間進行低溫的恆溫處理。本高錳鋼經1100℃固溶處理後，於沃斯田體基地內有條狀的麻田散體組織存在。此麻田散體可分為兩類：一為具FCC結晶結構的微小雙晶；另一為具HCP結晶結構的麻田散體。此麻田散體可一直存在於經低溫時效處理後的高錳鋼內。
經800℃以下溫度恆溫處理的高錳鋼內，於沃斯田體晶界處有M3C碳化物的析出。此M3C碳化物的析出上限溫度應介於825至800℃的溫度區間。於775至675℃的溫度區間，M3C碳化物除了以晶界析出物的形式出現外，亦以層狀晶粒方式成長進入沃斯田體基地內，與鄰近沃斯田體晶粒共同組成層狀組織，此種相變化型式稱為層狀反應，為析出反應的一種特殊形式。於700℃以下時，M3C碳化物亦以板狀魏德曼組織的形式出現，其於沃斯田體的晶界處出現並向沃斯田體基地的晶粒內生長。當溫度低於650℃時，於沃斯田體基地可觀察到波來體組織的存在，此為飽和的沃斯田體經由共析反應而分解為層狀肥粒體與M3C碳化物晶粒組成的板層狀交替的波來體組織。
本高錳鋼的沃斯田體基地有二種分解反應。當溫度高於675℃時，過飽和的沃斯田體會分解成較穩定的沃斯田體與M3C碳化物晶粒，而反應生成物的M3C碳化物的形式可能為晶界M3C碳化物，M3C+的層狀組織，或是M3C魏德曼組織。當溫度低於650℃時，於沃斯田體基地內會發生共析反應，部份沃斯田體晶粒分解成由肥粒體與M3C碳化物所組成的波來體。此二種相變化的區隔溫度是於675與650℃之間。

The object of this thesis is to study the phase transformations of a high manganese after being solution heated at 1100℃, and isothermally held at low temperatures from 825 to 500℃. The constituent phase of the steel at 1100℃ is single austenite. However, some irregular martensitic plates appear in the austenitic matrix during the high temperature cooling. The martensitic phases are composed of HCP -martensite and FCC micro-twins. The formation mechanism for both phases is due to the different stacking sequences of the stacking faults which is the results of the gliding of Shockley partial dislocations. The martensitic plates appear in the austenitic matrix even after the low-temperature heat treatment.
At temperatures below 800℃, there are grain boundary precipitates distributed along the austenitic grain boundaries. We confirmed that the precipitate is M3C carbide after the TEM study. In addition to the grain boundary precipitate, M3C carbide also appears in the austenitic matrix in the form of lamellae which are composed of both austenite and M3C grains. It is a special kind of precipitation transformation, in the name of cellular reaction. The upper temperature limit for the precipitation of M3C carbide in the high manganese steel is between 825 and 800℃. At temperatures below 700℃, we also observed the Widmanstatten side-plates appear in the austenitic matrix, and confirmed the crystal structure of the side-plates is M3C carbide by TEM. Thus, the M3C carbide is involved in three different morphologies in the austenitic matrix, i.e. grain boundary precipitates, lamellar M3C grains, and Widmanstatten side-plates.
We found traditional pearlite appear in the austenitic matrix at temperatures below 650℃. It is a eutectoid reaction for the decomposition of supersaturated austenite into ferrite and M3C carbide. The reaction product is in the form of lamellae. Due to the high content of Mn, the eutectoid temperature is lower, and is between 675 and 650℃ in the Mn-Al steel.

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