鐵鋁錳碳, 鐵鋁錳矽碳和鐵鋁鎳碳合金相變化

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 儀（EDS），研究鐵-8.0鋁-31.5錳-1.05碳、鐵-9鋁-30錳-2.0碳、鐵-9.0 鋁-30.5錳-(0-2.5)矽-1.2碳和鐵-8鋁-5鎳-2碳合金之相變化。本論文所 得結論如下：(一) 鐵-8.0鋁-31.5錳-1.05碳合金在淬火狀態下為單一沃 斯田鐵相。當此合金於550℃做時效處理後，在沃斯田 鐵晶界與雙晶 界可觀察到γ→γ+κ相碳化物的相分解反應。此結果與其他學者在 鐵-(4.9-11)鋁-(28.5- 34.3)錳-(0.50-1.62)碳合金所觀察的截然不 同，依合金成份不同，他們發現合金在550℃-650℃時效後會 有γ→ α+β-Mn、γ→α+β-Mn+κ、γ→β-Mn等的相分解反應。(二) 鐵-9 鋁-30錳-2碳在淬火狀態下，其顯微結構為沃斯田鐵相與細微κ'碳化物的 混合。其中細微κ'碳化物 是在淬火過程中藉由史賓諾多相分解反應 產生，此合金在550℃至750℃時效處理後，我們發現細小的κ' 碳化 物在沃斯田鐵基地內沿<100>方向成長及晶界可觀察到γ→γ+κ相碳化物 的相變化。將此合金在850 ℃至950℃溫度範圍內時效處理時，在沃 斯田基地內可觀察到極細的κ'相與粗大的κ'相及晶界可觀察到 γ →γ+粗大κ相+細小的κ相；其中極細的κ'相和細小的κ相是在淬火過 程中藉由史賓諾多相分解反應 產生。而在晶界粗大κ-相在650℃以 下是L'12結構，在750℃以上κ-相則是L12的結構，這些結果其他學 者研究結果截然不同。(三) 矽元素添加對鐵鋁錳碳合金相變化影響方面 。我們發現矽元素添加在鐵-9.0鋁-30.5錳-1.2碳合金中，會 促使 κ'-碳化物於淬火過程中藉由史賓諾多分解反應於沃斯田鐵基地內整合析 出。若矽元素添加量超過 1.5wt％時，亦會促使(α＋D03)相在沃斯 田鐵晶界上產生，其中D03相是藉由α→B2→D03連續規律化於 淬火 過程中形成。(四) 最近我們發現Fe-8Al-5Ni-2C合金在淬火狀態下，其 顯微結構為：沃斯田鐵相＋細微κ' 碳化物；其中 κ'-碳化物乃是 在淬火過程中，於沃斯田鐵基地內，以史賓諾多分解反應變態形成。當此 合金在550℃ 做時效處理後，此κ'-碳化物是沿著<100>方向成長。 另外，當增加時效處理時間後，在晶界上產生了 γ→κ＋B2＋α的 相分解反應。此結果與 W.K. Choo 等人相同合金成份之相變化的論文結 果截然不同。 The phase transformations in the Fe-8.0Al-31.5Mn-1.05C, Fe-9Al-30Mn-2.0C, Fe-9.0Al-30.5Mn-(0-2.5)Si-1.2C, Fe-8Al-5Ni-2C, have been examined by means of OM, STEM and EDS. As a result the following conclusions have been presented.(1) When the Fe-8.0 Al-31.5Mn-1.05C alloy was solution heat-treated and quenched, the microstructure was single-phase austenite. After being aged at 550℃, a γ→γ+κ-phase transition had occurred on the grain boundaries and twin boundaries. This result is quite different from that observed by other workers in the Fe-(4.9-11) wt pct Al-(28.5-34.3) wt pct Mn-(0.50-1.62)wt pct C alloys. In their studies, they found that when the alloy was aged at temperatures ranging from 550℃to 650℃, aγ→α+β-Mn, γ→ α+β-Mn+κand γ→ β-Mn reaction occurred on the grain boundaries.(2) In the as-quenched condition, the microstructure of Fe-9Al-30Mn-2.0C alloy was a mixture of (γ+κ'- carbide). When the alloy was aged at temperatures ranging from 550 ℃ to 750 ℃, fine κ'-carbides existing in the as- quenched austenite matrix grew preferentially along <100> directions and a γ→γ+κ-phase transition had occurred on the grain boundaries. When the aging temperature was in the range from 850℃ to 950℃, both coarse κ' and fine κ'- carbides could be observed within the austenite matrix . In the grain boundaries, a γ→ γ+coarse κ-carbide + fine κ- carbide transition had occurred on the grain boundaries. It is worthy to note that the κ-phase carbide has L'12-type structure at 650℃ or below and has an L12 type structure at 750℃ or above. These results are quite different from those reported by other workers in various Fe-Al-Mn-C alloys.(3) The effects of Si addition on the as-quenched microstructure of Fe-9.0Al-30.5Mn-1.2C alloy have been investigated. The results indicated that Si addition would enhance the κ'- carbides to precipitate coherently within the austenite matrix during rapid quenching by spinodal decomposition. With increasing the Si content to 1.5wt.%, (α+ D03) phases were also formed on the austenite grain boundaries in addition to the formation of the κ'-carbides within the austenite matrix. The D03 phase was formed during quenching by a α→B2→ D03 continuous ordering transition. (4) In the as-quenched condition, the microstructure of the alloy was austenite phase containing fineκ'-carbides. Theκ' carbides were formed during quenching by a spinodal decomposition. When the as- quenching alloy was aged at 550℃for short times, theκ'- carbides grew along <100> directions. After prolong aging at this temperature, aγ→α+B2+κ reaction occurred on the austenite grain boundary. This result is different from that observed by Choo and Kim in the same alloy.