鐵-10.0鋁-30.5錳-2.0碳合金相變化

Abstract

我們利用光學顯微鏡, 穿透透式電子 顯微鏡以及能量散怖儀,研究 鐵-10.0鋁-30.5錳-2.0碳合金相變化.在淬火狀態下其顯微結構為沃斯田 鐵相與細微k'相的混和其中細微k'相是在淬火過程中以spinodal decomposition 產生,具有L'12結構 當此合金在550c至750C時效處理 後,我們發現細小K'相碳化物在沃斯田鐵基地內沿100方向成長將此合金 在850C至950C溫度換範圍內時效處理時,在沃斯田鐵基地內可觀察到極細 的K'相與粗大的K'相;其中極細的K'相是以Spinodal Decomposition 在淬 火過程中形成.當時效溫度提高至1050C其顯微結構為單一沃斯田些鐵相 另外當合金在550c時效處理時晶界上有r-D03+K 的反應而在650C時效晶界 上則產商生r-r+k的反應,當時效溫度提高至750C時,晶界上除了有r-r+k 的反應外,晶界上的沃斯田鐵區域內尚有由 Spinodal Decomposition 所 產生的細小k碳化物.另外k相在650C以下是L'12結構,在750C以上K相則是 L12結構, 這些結果與其他學者研究結果截然不 同. Phase transformations in the Fe-10.0Al-30.5Mn-2.0C alloy have been investigated by using optical (OM),(TEM) and (EDS).In the as-quenched condition,the microstructure of the alloy was austenite phase containing extremely fine k'carbidesThe k' carbide has an L'12 type structure,which was formed within the austenite matrix during quenching by spinodal decomposition. When the alloy was aged at temperatures ranging from 550C to 750C , fine k' carbides existing in the as-quenched austenite matrix grew preferentially along100 directions.When the aging temperature was in the range from 850 to 950C, both coarse k' and fine k' carbides could be observed within the austenite matrix. The fine k'carbides were formed by spinodal decomposition during quenching.The microstructure of the alloy at 1050C or above is a single austenite phase. When the alloy was aged at 550C or below, a r-D03+k-phase transition occurred on the austenite grain boundary. With increasing the aging temperature to 650Ca r-r+k transition occurred on the grain boundary. Moreover, when the specimen was aged at 750C or above, not only a r-r+k transition occurred on the grain boundaries, but also extremely fine k' carbides formed within the austenite region ( on the grain boundaries) by spinodal decomposition during quenching. It is worthy to note that thek phase has L'12 type structure at 650 or below and an L12 type at 750or above. These results are quite different those reported by other workers in various Fe-Al-Mn-C alloys.