鐵-9.5鋁-30.0錳-5.0鉻-1.5碳合金之相變化

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-9.5鋁-30.0錳-5.0鉻-1.5碳之相變化。 在澆鑄狀態下，此合金的顯微結構為γ+κ'+κ+D03的混合相。在淬火狀態下，其顯微結構為沃斯田鐵相與細微κ'相的混和。其中細微κ'是在淬火過程中以史賓諾多節點分解反應（Spinodal Decomposition）產生，具有L'12結構。 當此合金在550℃時效處理後，我們發現κ'相碳化物在沃斯田鐵基地內沿＜100＞方向成長，在晶界上並未觀察到有析出物存在；在650℃時效處理後，不但在沃斯田鐵基地的κ'相碳化物成長，而且在晶界上有晶粒狀的κ相碳化物和板狀的β-錳析出；在750℃時效後，沃斯田鐵基地為κ'相和D03的混合相，其中D03相是在淬火過程中經由α→B2→D03的序化反應產生的，晶界上則仍為κ相碳化物和β錳；在850℃時效後，在沃斯田鐵基地可發現粗大的κ'相碳化物，晶界上則有α和κ相析出；在950℃以上時效，僅能在沃斯田鐵基地中觀察到細微的κ'相碳化物，晶界則無析出，這與淬火狀態下的顯微結構相似。所以，隨著溫度由550℃至850℃，晶界上的反應為γ→κ相+β-錳→α相+κ相→γ。

Phase transformations in the Fe-9.5Al-30.0Mn-5.0Cr-1.5C alloy has been examined by means of optical microscopy(OM), transmission electron microscopy(TEM) and energy-dispersive X-ray spectrometer(EDS). In the as-cast condition, the microstructure in the present alloy is the mixture of theγ+κ'+κ+D03-phases. When the alloy was solution heat-treated and then quenched, the microstructure of the alloy was austenite phase containing extremely fine (Fe,Mn)3AlCx carbides (κ'-carbides). Theκ'-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 550℃, theκ'-carbides existing in the as-quenched austenite matrix grew preferentially along ＜100＞ directions, but no grain boundary precipitates could be observed. When the alloy was aged at 650℃, not only theκ'-carbides grew within the austenite matrix but also some plate-likeβ-Mn and granular-shaped κ-carbides precipitated on the grain boundaries. When the alloy was aged at 750℃, the microstructure within the matrix was the mixture of κ'-carbide and D03 phase. The D03 phase was formed by a α→B2→D03 continuous ordering transition during quenching. Moreover, the β-Mn precipitates and κ-carbides were formed on the grain boundaries. When the alloy was aged at 850℃, the coarseκ'-carbides could be observed within the austenite matrix, in addition, the precipitation of (α+κ) phases also occurred on the grain boundaries. When the alloy was aged at 950℃, only extremely fineκ'-carbides could be detected within the austenite matrix and no grain boundary precipitates could be examined, which was similar to that found in the as-quenched alloy. Therefore, when the alloy aged at temperatures ranging from 550℃ to 850℃, the phase transition sequence as the temperature increase was found to beγ→κ-phase +β-Mn→α-phase +κ-phase →γ.