本論文針對鐵-20鎳4.5鋁1.0碳(wt.%)四元合金鋼經不同熱處理後發生的相變化機制以及其組成相進行分析。1100℃進行持溫一小時後用水淬火至室溫的固溶處理後的合金鋼為單一沃斯田體相(γ)。經由500℃至1000℃的恆溫處理後，均可觀察到由沃斯田體相發生析出型相變化後均勻析出的有序富鎳鋁B2相。低於650℃的恆溫處理，在沃斯田體基地析出經由spinodal相分離和有序化相變化後的有序L12富碳相，此相的成分為(Fe,Ni)3Al。此外，900℃至700℃的恆溫處理會出現麻田散體相，其原因是周圍B2大量析出使基地內鎳含量明顯下降，麻田散體形成溫度(Ms)上升而在冷卻過程中出現；650℃與600℃出現的麻田散體相是因碳化物大量析出使基地碳含量降低，Ms溫度提高而形成。700℃以下有發現M23C6與M3C碳化物的析出。經實驗推論BCC晶粒在300℃時為貧鎳鋁BCC相(α_1)與富鎳鋁BCC相(α_2)的雙相結構，此原因為高溫BCC相(α)在300℃時經spinodal相分離成(α_1+α_2)兩相，在冷卻至室溫的過程中，兩相分別發生spinodal相分離以及有序化反應，各自形成BCC+B2雙相。

The phase transformation mechanisms in an Fe-20Ni-4.5Al-1.0C(wt.%) quartenary alloy have been studied by high temperatures solution treatment and isothermal holding at low temperatures for various holding times. The results show that the alloy has a single Face Centered Cubic (FCC) austenite phase (γ) after solution treatment. Ordered B2 phase was observed at aging temperatures between 500℃ to 1000℃. At aging temperature below 650℃, ordered (Fe,Ni)3Al L12 phase was observed. This phase was formed by transformation of γ into L12 phase via spinodal decomposition and ordering reaction. Martensite structure was observed in samples at aging temperatures ranging from 900°C to 700°C. This martensite could have formed during alloy cooling as a result of precipitation of B2 phase which led to decrease in nickel content of the surrounding matrix thereby increasing martensite start temperature (Ms). At 650°C and 600°C, martensite could have formed because of carbides, which reduced the local carbon content thereby increasing Ms. The M23C6 and M3C carbides were found to precipitate at aging temperatures below 650℃. Two body centered cubic (BCC) phases, α_(1 )and α_2 which are lean and rich in Ni-Al respectively, were found to be present in the sample aged at 300℃ for 100h by spinodal decomposition. α1 and α2 undergoing spinodal decomposition and ordering reaction upon cooling to lower temperature to form BCC and B2 phases.

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