鐵-9鋁-30錳-2.5鉻-0.6碳合金之相變化

Abstract

我們使用掃描式電子顯微鏡(SEM)、穿透式電子顯微鏡(TEM)與X光能量散佈分析儀(EDS)，研究鐵-9鋁-30錳-2.5鉻-0.6碳合金的相變化。 鐵-9鋁-30錳-2.5鉻-0.6碳合金在淬火狀態下之顯微結構是沃斯田鐵相(γ)與肥粒鐵(α)相的雙相結構。藉由電子繞射技術證實於固溶淬火過程中沒有任何析出物在沃斯田鐵相與肥粒鐵相之中產生。在650℃的溫度下進行不同時間的時效處理後，在時效處理初期，我們觀察到沃斯田鐵相中並無任何析出，但是在肥粒鐵相的基地中發現生成D03 相與M23C6及M5C2 兩種碳化物。隨著時效時間的增加，在沃斯田鐵相的基地中生成κ' carbide此碳化物，此外，β-Mn相也在肥粒鐵相的基地中形成。在我們的認知當中，具有單斜結構(monoclinic structure)的M5C2碳化物是第一次在鐵鋁錳合金系統中被觀察發現，而且此M5C2碳化物與D03相和β-Mn相共存，這是從未被發現過的情形。此一研究結果與鐵-8.8鋁-30錳-6鉻-1.0碳合金與鐵-8.8鋁-30錳-2.5鉻合金等文獻的結果有相當大的不同。

Phase transformations in an Fe-9Al-30Mn-2.5Cr-0.6C alloy have been examined by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectrometry (EDS). In the as-quenched condition, the microstructure of the alloy was (austenite + ferrite) dual-phases. No precipitate was found within the ferrite phase and austenite phase in the as-quenched specimen, which was confirmed by the electron diffraction method. When the alloy was aged at 650℃, the phase transformation sequence as the aging time increased was found to be [γ + α] → [γ + (α + D03 + M23C6 + M5C2)] → [(γ + κ' carbide) + (α + D03 + β-Mn + M23C6 + M5C2)]. It is noted that, the monoclinic type M5C2 carbide has not been observed by other workers in Fe-Al-Mn alloy systems before. In addition, the coexistence of M5C2 carbide, D03 and β-Mn has also never been reported in the previous literatures. These results are quite different from the previously observations in the Fe-8.8Al-30Mn-6Cr-1.0C alloy and Fe-9.1Al-29.9Mn -2.9Cr alloy.