鐵-9.0鋁-31.2錳-1.6碳合金相變化

Abstract

我們利用光學顯微鏡(OM)，X光能量分析儀(EDS)以及穿透式電子顯微鏡( TEM)等,研究鐵-9.0鋁-31.2錳-1.6碳合金之相變化。在淬火狀態下其顯微 結構為沃斯田鐵相＋細微的κ'-相碳化物，此κ'-相碳化物是在淬火過程 中於沃斯田鐵基地內以節點分解(Spinodal Decomposition)變態形成。且 具有L'12的結構。這種現象從未被其他鐵鋁錳碳合金研究者發現過。當此 合金在550℃至850℃時效處理後，在淬火過程中於沃斯田鐵基地形成的細 微κ'-相碳化物會沿<100>方向成長。增加時效處理時間，在晶界產生γ →γ＋κ-相的分解反應。這些結果和其他學者所觀察的現象截然不同。 更值得注意的是，此合金經750℃或低於750℃作時效處理，κ-相碳化物 為 L'12結構，而在850℃作時效處理時為L12結構。在950℃作時效處理時 ，在晶界可以看到一些粗大的κ-相碳化物並且在沃斯田鐵基地內有淬火 過程中經由節點分解(Spinodal Decomposition)變態產生的細微κ'-相碳 化物。這種現象從未被其他學者發現過。 Phase transformations in the Fe-9.0Al-31.2Mn-1.6C alloy have been investigated by using optical microscopy (OM), transmission electron microscopy (TEM) and energy-dispersive X- ray (EDS).In as-quenched condition, the microstructure of the alloy was austenite phase containing (Fe,Mn)3AlCx({SYMBOL 107 \f {SYMBOL 162 \f "Symbol"}-phase) carbides.The {SYMBOL 107 \f {SYMBOL 162 \f "Symbol"}carbide has an L{SYMBOL 162 \f 12-type structure, which was formed within the austenite matrix during quenching by spinodal decomposition.This feature has never been observed by other workers in various Fe-Al-Mn-C alloys. When the alloy was aged at temperature ranging from 550 {SYMBOL 176 \f "Symbol"}C to 850{SYMBOL 176 \f "Symbol"}C, fine {SYMBOL 107 \f "Symbol"}{SYMBOL 162 \f "Symbol"}- carbides existing in the as-quenched austenite matrix grew preferentially along <100> directions.Prolonged aging at the same temperature range, a {SYMBOL 103 \f "Symbol"} {SYMBOL 174 \f "Symbol"} {SYMBOL 103 \f "Symbol"} + {SYMBOL 107 \f "Symbol"}-phase reaction could be found on the austenite grain boundaries is quite different from that observed by other workers in the Fe-Al-Mn-C alloys.It is worthy to note that the {SYMBOL 107 \f "Symbol"}-phase carbide has an L{SYMBOL 162 \f "Symbol"}12-type structure at 750 {SYMBOL 176 \f "Symbol"}C or below and an L12-type structure at 850{SYMBOL 176 \f "Symbol" }C.When the alloy was aged at 950 {SYMBOL 176 \f "Symbol"}C, some coarse {SYMBOL 107 \f "Symbol"} -phase carbides could be observed on the grain boundaries. Furthermore,extremely fine {SYMBOL 107 \f "Symbol"} {SYMBOL 162 \f "Symbol"} carbides could also be found within the austenite matrix by spinodal decomposition during quenching. This feature has never been found by other workers.