本論文為研究鐵-14.8錳-3.4鋁-1.0碳(wt%)之錳鋁鋼經不同溫度的熱處理後所產生的相變化情形。熱處理方式為高溫1100℃固溶處理以及於800至500℃的溫度範圍分別進行低溫恆溫處理。
錳鋁鋼經1100℃固溶處理後，其相組成為沃斯田體基地相以及分布於沃斯田體基地內之條狀麻田散體相。此麻田散體為具FCC結晶結構的微小雙晶。此麻田散體可一直存在於經低溫時效處理的錳鋁鋼內。當溫度介於800至725℃時，並無任何的析出物出現；因此可知本錳鋁鋼在1100至725℃之溫度區間為單相的沃斯田體。當錳鋁鋼於700℃時， M3C碳化物析出於晶界處。故此碳化物的析出上限溫度應介於725至700℃的溫度區間內。
當溫度於675℃以下時，波來體組織已經均勻的散佈在合金內。經TEM的觀察發現，此由層狀碳化物與肥粒體晶粒所共同組成的波來體組織，其碳化物可以分別具有二種不同的晶體結構，亦即M3C或是M23C6碳化物，所以本研究發現於此錳鋁鋼內，M3C波來體與M23C6波來體是有共存的情形。
於本錳鋁鋼內的M3C波來體，層狀M3C碳化物與肥粒體晶粒間具有下列7種的方位關係：1. [010]C // [1 ‾11]α, (103)C // (110)α；2. [31 ‾1 ‾]C // [1 ‾11]α, (022)C // (110)α；3. [100]C // [11 ‾2]α, (022)C // (110)α；4. [101 ‾]C // [01 ‾1]α, (121)C // (011)α；5. [010]C // [113 ‾]α, (103)C // (11 ‾0)α；6. [121]C // [012]α, (303 ‾)C // (121)α；7.[111]C // [110]α, (022)C // (110)α。而於M23C6波來體內，M23C6與肥粒體晶粒間，發現兩組方位關係：一為[01 ‾1]C6 // [001]α, (111)C6 // (110)α；而二為[01 ‾1]C6 // [1 ‾11]α, (111)C6 // (110)α。

We have studied the phase transformations of a Mn-Al steel after it was heated at 1100℃ for solution heat treatment and followed by isothermal holding for 100 h at temperatures between 800 and 500℃. The composition of the steel is Fe-14.8 Mn-3.4 Al-1.0 C (wt%).
The constituent phase of the steel at temperatures between 1100 and 725℃ is single austenite. Irregular martensitic plates exist in the austenitic matrix after cooling. They are FCC micro-twins. At a temperature of 700℃, grain boundary M3C carbide precipitates in the austenitic grains. Thus, the upper temperature for the appearance of M3C carbide is between 725 and 700℃. We found that kappa carbide appears at the austenitic grain boundaries for the steel being isothermally held at 675℃. The appearance of the kappa phase is probably due to the high content of Al in the Mn-Al steel. For the steel held at the same temperature, we observed two different pearlites coexisting in the austenitic matrix. One pearlite is composed of lamellar grains of ferrite and M3C carbide, and the other is composed of lamellar grains of ferrite and M23C6 carbide. They are from two separate eutectoid reactions, decomposing supersaturated austenite into lamellae of ferrite and carbide. The carbide could be either M3C or M23C6.
We discovered several orientation relationships between two adjacent grains with different crystal structures. Between M3C and ferrite grains: 1. [010]C // [1 ‾11]α, (103)C // (110)α; 2. [311 ‾]C // [1 ‾11]α, (022)C // (110)α; 3. [100]C // [11 ‾2]α, (022)C // (110)α; 4. [101 ‾]C // [01 ‾1]α, (121)C // (011)α; 5. [010]C // [113 ‾]α, (103)C // (11 ‾0)α; 6. [121]C // [012]α, (303 ‾)C // (121)α; 7.[111]C // [110]α, (022)C // (110)α. Between M23C6 and ferrite grains: [01 ‾1]C6 // [001]α, (111)C6 // (110)α; and [01 ‾1]C6 // [1 ‾11]α, (111)C6 // (110)α.

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