低碳鋼為產量最高之鋼品，且其延韌性、成型性以及可焊性皆優於中高碳鋼；由於其麻田散體相變態不易，以往被視為非熱處理型鋼鐵材料而僅用於強度要求較低之場合，如包裝用鋼帶。其中AISI 1013低碳鋼由於錳含量較高，可誘使麻田散體變態溫度下降，經充份沃斯田體化後淬火可生成大量高強度之板條狀麻田散體；於此基礎上，本研究分別利用淬火、淬火回火、沃斯回火以及淬火中斷此四種淬火及回火相關之熱處理方式，改變1013低碳鋼之微觀組織，並探討其對機械性質造成之影響，以期獲得適當之機械性質表現，進而拓展低碳鋼應用範圍。
於1100℃沃斯田體化30分鐘後淬火可使1013低碳鋼獲得約75%之大量板條狀麻田散體，抗拉強度可達1200MPa；且低碳鋼由於有自回火效應，於淬火過程中即可使板條狀麻田散體內部析出微細雪明碳體顆粒，藉此消耗麻田散體中部份過飽和碳，使其保有5%之TE。
若於淬火後再施以回火熱處理，1013低碳鋼之強度不但降低至1000MPa以下，其延性亦下降，此乃因回火過程使板條狀結構逐漸分解，且使細小自回火碳化物粗大化；其中260℃長時間回火熱處理後甚至可明顯觀察到粗大化之雪明碳體廣泛分佈於回火麻田散體基地中，造成延性無法改善。推論一般回火熱處理不適用於1013低碳鋼。
而於550℃持溫30分鐘進行沃斯回火熱處理後可獲得肥粒體及碳化物顆粒之混合組織，抗拉強度約為480MPa，且延性相當優良，TE達近20%，合乎某些建構用鋼材之規範。然而，受限於低碳鋼合金成份較少，導致I-T圖中波來體與變韌體相變態之C型曲線重疊，不利於變韌體相變態，故沃斯回火熱處理無法使1013低碳鋼獲得大量變韌體組織。
將近年來新發展的淬火中斷熱處理方式應用於1013低碳鋼，可使原本不具備強度優勢之低碳鋼獲得高強度並保有相當程度之延性。透過260℃第一階段淬火生成高強度之板條狀麻田散體，再以第二階段450℃中斷熱處理持溫10分鐘，使得原本過飽和固溶於麻田散體中之碳以奈米級碳化物方式析出於基地之中，透過TEM鑑定其為過渡性碳化物ε-carbide。這些微細碳化物廣泛析出於基地之中，可藉此消耗板條狀麻田散體之過飽和碳，而使淬火中斷熱處理後延性得以提高到9.4%；且透過部份麻田散體基底及碳化物分散強化之效果，使得拉伸強度可高達近700MPa。
實驗結果顯示，淬火組具有1200MPa以上超高強度之特性並保有些許延性；淬火回火組之強度可高達約1000MPa，但延性低於淬火組；沃斯回火組之強度則較低，約480MPa，而延性相當優異，約達20%；淬火中斷組則較為平衡，強度達約700MPa並保有近10%之延性。整體而言，透過適當之熱處理，能夠大幅增加1013低碳鋼之優勢及應用範圍。

The yield of low carbon steel is more than other different kinds of steel. In spite of the good performance in ductility, formability and weldability, it has been considered as non-heat treatable steel since it is insensitive to the martensitic transformation and thus only used for the applications which the strength requirement is relatively low, like steel strip. One specific low carbon steel, named AISI 1013, is composed of additional Mn, which can lower the martensitic transformation temperature effectively. Therefore, a lot of lath martensite structure can be obtained to contribute to strength after adequate austenitizing and quenching. In this study, quenching, quenching & tempering (Q&T), austempering and quenching & partitioning (Q&P) are used as heat treatment to affect not only microstructure features but also mechanical properties of 1013 low carbon steel. The intent of this study is to acquire appropriate mechanical properties which can expand the applications of low carbon steel.
1013 shows a very high strength about 1200MPa in UTS with more than 75% lath martensite in volume after quenching from austenitization for 30 minutes at 1100℃. Because of the autotempering effect of low carbon steel, the fine cementite particles which precipitate in lath martensite during quenching and consuming the supersatured carbon is favorable to the ductility, which is about 5% in TE.
Not only the strength but the ductility becomes worse after tempering than as-quenched. During tempering treatment, the lath marteniste structure turns to decompose and the autotempered carbide particle tends to be coarsening. When it comes to long time tempering at 470℃, the coarse cementite particles can be observed in the tempered martensite matrix clearly. As a result, the ductility cannot be improved after Q&T heat treatment. The Q&T heat treatment may not be so suitable for 1013 low carbon steel.
The microstructure of 1013 low carbon steel is a mixed structure of ferrite and carbide after austempering heat treatment for 30 minutes at 550℃. The strength is about 480MPa with outstanding ductility which is almost 20% in TE and satisfies with some specifications of the construction material. However, there is almost no bainite in the microstructure after austempering due to less additional element in low carbon steel, which leading to the superposition of C curve in I-T diagram and thus hindering the bainite formation.
Applying the new concept of heat treatment, which called “Quenching & Partitioning”, to 1013 low carbon steel can acquire high strength with acceptable ductility instead of the nature poor strength of low carbon steel. It consists of high strength lath martensite after quenching from 260℃, then precipitates the nano carbides in the matrix after partitioning for 10 minutes at 450℃ by the supersaturating carbon of martensite. These carbides are identified as ε-carbide according to TEM results. The excess carbon in lath martensite is consumed by the wide precipitation of fine carbides and thus improves the ductility to 9.4% in TE. High strength of martensite matrix and dispersion strengthening of fine carbide particles contributes to high strength which the UTS is nearly 700MPa after Q&P heat treatment. The application of 1013 low carbon steel is thus expanded by good performance in mechanical properties after suitable heat treatment.

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