鐵-12.0鋁-30.0錳-1.2碳合金相變化

Abstract

我們利用光學顯微鏡(OM)、穿透式顯微鏡(TEM)以及X-光能量散佈儀(EDS) ， 研究鐵-12.0鋁-30.0錳-1.2碳合金之相變化。在淬火狀態下，其顯微 結構為沃斯 田鐵相與細微κ*相的混合。其中細微κ*相是在淬火過程中 以Spinodal Decomposition產生，具有L*12結構。 當此合金在550℃ 至750℃時效處理後，我們發現細小的κ*相碳化物在淬火 狀態之試片內 沿<100>方向成長，此κ*相亦具有L*12結構。然而，時效溫度提高 至850 ℃-950℃，在沃斯田鐵基地內可觀察到成長之κ*相具有L12結構。當時效 溫度提高到1050℃時，其顯微結構為單一沃斯田鐵相。 另外，當合金 在550℃時效處理時，晶界上有γ*D03+κ的反應，此κ相亦 為(Fe,Mn)3 AlC碳化物。為了方便起見，將κ*相與κ相分別表示形成在沃斯田鐵 基 地內及晶界上之(Fe,Mn)3AlC碳化物。此γ*D03+κ相分解變態在鐵鋁錳碳 四 元合金中未被發現過；而在750℃時效時，晶界上有γ*B2+κ的反應。 當時效 溫度提高至850℃時，晶界上則產生γ*α+κ的反應。另外κ相 在750℃以下 是L*12結構，在850℃以上κ相則是L12結構。 Phase transformations in the Fe-12.0Al-30.0Mn-1.2C alloy have been examined by means of optical microscopy (OM) , transmission electron microscopy (TEM) and energy-dispersive X- ray spectrometer (EDS) . In the as-quenched condition , the microstructure of the alloy was austenite phase containing extremely fine (Fe,Mn)3AlC (κ*-carbides) . The κ*-carbides having an L*12-type structure were formed within the austenite matrix during quenching by spinodal decomposition . When the alloy was aged at temperatures ranging from 550℃ to 750℃ , fine κ*-carbides existing in the as-quenched specimen grew preferentially along <100> directions . The κ*-carbides have also an L*12-type structure . However , when the aging temperature was increased to 850℃-950℃ , the well-grown κ*- carbides within the austenite matrix have an L12-type structure . The microstructure of the alloy aged at 1050℃ or above is a single-phase austenite . When the alloy was aged at 550℃ , a γ*D03+κ-carbide transition occurred on the austenite grain boundaries . The κ-carbide is also (Fe,Mn)3AlC carbide . For convience , the κ* and κ-carbides represent the (Fe,Mn)3AlC carbide formed within the austenite matrix and on the grain boundary , respectively . It is noted here that the γ*D03+κ- carbide transition has never before been observed by other workers in the Fe-Al-Mn-C quarternary alloy . With increasing the aging temperature to 750℃ , a γ *B2+κ-carbide transition occurred on the grain boundaries . When the specimen was aged at 850℃ or above , a γ*α+κ-carbide transition occurred on the grain boundaries . It is worthy to note that the κ-carbide has an L*12-type structure at 750℃ or below and an L12-type structure at 850℃ or above .