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題名 | 沃斯回火延性鑄鐵之熱處理與相變態機構=Heat Treatment and Phase Transformation Mechanism of Austempered Ductile Iron |
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作 者 | 張柳春; | 書刊名 | 材料科學 |
卷期 | 30:4 1998.12[民87.12] |
頁次 | 頁253-268 |
分類號 | 440.363 |
關鍵詞 | 沃斯回火延性鑄鐵; 沃斯回火熱處理; 變韌鐵; 殘留沃斯田鐵; 製程窗口; Austempered ductile iron; ADI; Austempering heat treatment; Bainite; Retained austenite; Processing window; |
語文 | 中文(Chinese) |
中文摘要 | 具優良機械性質與耐磨耗性的沃斯回火延性鑄鐵已成為重要的工程材料。本文回 顧了沃斯回火熱處理各程序之物理冶金原理,並以熱力學與相變態理論剖析文獻所報導之各 現象。沃斯回火熱處理的第一階段反應為沃斯田鐵以麻田散鐵式的位移機構變態為變韌肥粒 鐵;隨後尚未變態之沃斯田鐵的分解則稱為第二階段反應。沃斯田鐵化溫度影響基地內之碳 含量 (C) 與變韌鐵變態之起始溫度 (Bs), 沃斯回火溫度則決定殘留沃斯田鐵的碳含量 (C γ ) ;參數 (C γ -C γ ) 直接關係到變韌鐵反應的自由能、生長速率與變韌肥粒鐵生成 量等,亦間接影響到殘留沃斯田鐵的數量。由於偏析的緣故,此種鑄鐵中各區域變韌鐵變態 時間與數量並不一致,為了獲得最佳的顯微組織,合金元素的添加至為重要:偏析於樹枝狀 晶包間的錳與鉬的添加量應低,而以鎳與銅等偏析於樹枝狀晶包的元素取代。本文並將探討 沃斯回火延性鑄鐵顯微組織之演進與控制。 |
英文摘要 | Austempered Ductile Iron (ADI) has become an important engineering alloy due to its outstanding combination of mechanical properties and wear performance. This paper reviews the physical metallurgy principles of austempered heat treatment, along with an analysis of the reported results in literatures using thermodynamics and phase transformation theory. It is well recognized that the first stage of austempered heat treatment is the formation of bainitic ferrite via a martensitic manner. It is followed by the decomposition of un-transformed austenite, the second stage reaction. Austenized temperature determines the initial carbon content in austenite (C) and therefore the bainite-start(Bs) temperature, while austempering temperature affects the final carbon concentration in retained austenite(C γ ). The parameter (C γ -C γ )beas significant implication in free energy change for bainite reaction, growth rate as well as the maximum extent of bainite can be obtained, which in turn affects the volume fraction of retained austenite. Chemical heterogeneity due to segregation results in differential bainite reaction timing for different area in ADI. In order to obtain optimum microstructures, alloying elements addition has to be carefully controlled:those alloying elements segregate into the dendrite, such as Mn and Mo, have to be minimized. On the other hand, Ni and Cu, which tend to segregate into inter-dendritic cell, can be increased. This present paper also deals the evolution and control of microstructure in ADI. |
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