鐵-9.0 鋁-30.0 錳-1.5 矽-2.0碳合金相變化

Abstract

我們利用光學顯微鏡（OM），穿透式電子顯微鏡（TEM）以及X-光能量散佈分析儀（EDS），研究鐵-9.0鋁-30.OMn-1. 5Si-2. OC合金之相變化。 在淬火狀態下，其顯微結構為沃斯田鐵相與細微K'相的混合。其中細微K'相是在淬火過程中以節點反應（Spinodal Decomposition）產生，具有L'l2結構。 當此合金在550°C至900°C時效處理後，我們發現K'相碳化物存在於沃斯田鐵基地與晶界上。隨著溫度由550°C至900°C，晶界上的反應為r→DO3+k相→B2+k相→a+k相。另外，K相在750°C以下為L'I2結構，在850°C以上則為LI2結構。當時效溫度提高到950°C，在沃斯田鐵基地內可觀察到極細的K'相跟粗大的K'相，其中粗大的K'相是在時效處理時產生，細小的K'相是在淬火過程中藉由節點反應產生。這種細小和粗大K'相同時析出現象，在鐵鋁錳合金內從未被發現過。

Phase Transformations in the Fe-9.0Al-30.0Mn-1.5Si-2.0C alloy have been examined by means of optical microscopy (OM), transmission electron microscopy (TEM) and energy-disopersive X-ray spectrometer (EDS). In the as-quenched condition, the microstructure of the alloy was austenite phase containing extremely fine (Fe,Mn)3ALCx (K'-carbides). the K'-carbides having an L'12-type structure were formed within the austenite matrix during quenching by a spinodal decomposition. When the alloy was aged at termperatures ranging from 550℃ to 990℃, the k'-carbides not only existed within the austenite matrix but also on the grain boundaries. The phase transition sequence as the temperature increases was found to be r→DO3 + k-phase→B2 +K-phase→a +K-phase. It is worthy to note that the k'-carbide has an L'l2-type structure at 750℃ or below and an Ll2-type structure at 850℃ or above. when the alloy was aged at 950, both the coarse and extremely fine k' carbides could be observed with the austenite matrix. The coarse k' carbides had occurred at the aging temperature; whereas the extremely fine k' carbides were of formed during quenching by a spinodal decomposition. The coesistence of the coarse and extremely fine k' carbides formed within the austenite matrix has never been observed by other workers in the Fe-Al -Mn-C alloy systems.