- 學位論文
連續澆鑄銅鈹冷卻輪之劣化機制研究
Investigation into the Formation Mechanism of Defects on the Surface of Cu-Be Cooling Wheel by Cyclic Planar Flow Casting Process
摘要
合金薄帶生產的過程中，冷卻銅輪(銅鈹合金C17200)基材受到熔融金屬鋼液的反覆熱衝擊後，其冷卻基材表面極容易形成熔損或pits等缺陷。為能了解冷卻銅輪缺陷形成原因，本研究以三種方式進行破損分析，包括(1)直接進行線上觀察(包含複製模與手持式OM檢測)、(2)進行模擬試驗與(3)對退役銅輪進行檢測等；經由上述分析方法發現，冷卻銅輪缺陷型態共分為主要破損型態及次要破損型態，而加工痕內Fe-Cu-O化合物所誘發的破損型態定義為主要破損型態，而Co-Be顆粒所誘發的破損型態定義為次要的破損型態；實驗證明，主要破損型態形成機制如下：高溫鋼液澆鑄時，冷卻轉輪表面氧化銅增加，氧化銅逐漸增加到一定程度後，表面濕潤性增加使得鋼液開始沾黏，鋼液中的鐵與銅輪氧化物進行反應形成Fe-Cu-O界面層，在澆鑄過程中，因研磨加工後所產生之表面應力層發生再結晶的細晶粒，少部分鋼液沾黏於Fe-Cu-O界面層，後續澆鑄過程中薄帶將鋼液、Fe-Cu-O界面層及銅細晶粒拔起，反覆上述程序加工痕空孔加大，部分缺陷結合形成較大之缺陷。 次要破損型態形成機制如下：澆鑄初期，銅輪表面氧化銅逐漸增加，氧化銅累積到一定程度，開始沾黏鋼液，鋼液與銅輪表面中的Co-Be顆粒進行反應，由於Co-Be顆粒與Cu基地結合性欠佳，容易在Co-Be邊緣產生破損，反應物及Co-Be周圍表層再結晶的小晶粒Cu合金在薄帶剝離時帶走，並開始形成小缺陷，當Co-Be周圍缺陷加大後被薄帶沾黏帶走並形成空孔，反覆上述程序，空孔加大， 並與周邊空孔結合形成較大之缺陷。
並列摘要
Continuous casting of ribbon is accomplished by cyclic deposition of molten alloy onto a casting cooling wheel (e.g. C17200 Be-Cu alloy) and rapid quench. The cyclic molten metal contact and remove the solidified ribbon from the casting surface may result in many types of defects on the surface of the casting cooling wheel, such as pits or melting penetration. To investigate interface reaction between Be-Cu (C17200) alloy and molten alloy, and the formation mechanism of the defects, in this study, three approaches were conducted, including: direct on-line observation (using replication tapes and portable optical microscopy), conduct the simulation test (using Be-Cu alloy was cyclically dipped into molten Fe/Si/B alloy various times), and direct inspection on the retired cooling wheel. After conducting the above tests, surface defects on the tested samples, microstructure and chemical composition of the reaction compounds in the tested samples were investigated. The test results showed that two types of defects, primary and secondary defects, can be found on the surface of the cooling wheel. The primary defect is so-called “machining groove induced defect”, the formation mechanism and sequence of the defect including the follows: 1.Surface oxidation accumulated in machining grooves during the earlier cyclical casting, 2. Molten alloy accumulated in machining grooves, 3. Fe/Cu/O compound was formed on the surface, 4. Also, re-crystallization occurred on the surface (Strengths reduction), 5. Fe/Cu/O compound was stripped by following casting, 6. After cyclical casting, the size of defects increased. The formation mechanism and sequence of the secondary defect including: 1. Surface oxidation during the earlier cyclical casting, 2. Molten alloy started to reacted to Co-Be particles, more surface oxidation formed, 3.Molten alloy became more easier to react with Co-Be particles, Co/Be-Fe-Cu-O may form, 4. Simultaneously, re-crystallization occurred on the surface (Strengths reduction), 5. Breakage occurred between Co-Be and matrix during the casting, 6. Co/Be-Fe-Cu-O was stripped by the following casting, 7. After cyclical casting, the size of defects increased.
參考文獻
延伸閱讀
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