銲接沃斯田鐵系不銹鋼為乾貯系統中的密封鋼筒的主要材料，用於貯存用過核子燃料，台灣的乾貯場址選在沿海地區，環境充滿水氣與氯離子，再加上銲接過程中產生的高殘餘張應力以及受敏化現象影響，容易在不銹鋼筒表面引發氯離子誘發應力腐蝕龜裂，當生成的裂縫足以裂穿筒身，將影響用過核子燃料貯存的安全性，因此本實驗希望透過模擬室內乾貯的環境，探討以沃斯田鐵系不銹鋼304L、316L為基材銲接308L、316L銲條所製成不銹鋼U-bend銲件在不同溫度下、固定相對濕度40%的腐蝕行為，並研究相關的腐蝕劣化因子關係。
實驗結果顯示在溫度40、60及80oC下， 304L/308L與316L/316L SS試片在基材區域與熱影響區的腐蝕形貌以大面積孔蝕的聚合為主，在銲材區域則以枝晶狀腐蝕與孔蝕的聚合為主。根據腐蝕面積的定量計算結果顯示，在溫度40與60oC下，隨著實驗時間增加，腐蝕面積比例上升的速率較80oC的結果快，推測可能是因為在溫度80 oC下，腐蝕在短時間內達到其飽和值。孔蝕深度的量測結果顯示在三種不同溫度下，316L/316L SS試片的基材區域皆有深度超過60μm的孔蝕出現。

Welded austenitic stainless steels are considered as the materials for dry storage canisters used for interim storage of spent nuclear fuel. However, austenitic stainless steels are susceptible to chloride induced stress corrosion cracking (CISCC), particularly in the presence of residual tensile stress and sensitization due to the welding procedure. Dry storage systems located nearby a coastal site in Taiwan, thus high concentration of moisture and chloride salts in the atmospheric environment may introduce CISCC on the canisters surface. Therefore, the purpose of this study is to evaluate the corrosion behavior of candidate canisters materials in a salt fog test at different temperatures and constant relative humidity of 40% for 1500 hours.
According to the results of morphology observation, similar corrosion behavior was observed on three different materials at 40, 60 and 80oC. Pitting coalescence was the major corrosion behavior on the base metal and heat affected zone, and interdendritic corrosion and pitting coalescence were the primary corrosion behavior on the weld metal. Based on the calculation of corroded area, the percentage of corroded area increased significantly at 40 and 60oC with time, whereas it was slightly expanded at 80oC. Moreover, the depth of pits up to more than 60μm were measured on the base metal of 316L/316L SS specimens at three different temperatures.

摘要 i
ABSTRACT ii
致謝 iii
目錄 v
表目錄 ix
圖目錄 x
第一章 前言 1
1.1 研究背景 1
1.2 研究動機 2
第二章 文獻回顧 3
2.1 乾式貯存系統的介紹 3
2.2 台灣現行乾貯設施 5
2.3 台灣乾貯筒環境 7
2.3.1 密封鋼筒表面溫度 7
2.3.2 密封鋼筒表面濕度 9
2.3.3 氯鹽沉積量 11
2.4 應力腐蝕龜裂 12
2.4.1 機制 13
2.4.2 應力腐蝕龜裂形成三要素 14
2.4.2.1 敏感性材料 14
2.4.2.2 足夠的張應力 16
2.4.2.3 腐蝕性環境 17
2.5 孔蝕 18
2.5.1 孔蝕的起始 19
2.5.2 孔蝕的成長 21
2.6 誘發應力腐蝕龜裂的影響因素 22
2.6.1 溫度的影響 22
2.6.2 相對濕度的影響 24
2.6.3 氯鹽種類的影響 28
2.6.4 氯鹽沉積量的影響 33
2.6.5 銲接的影響 35
第三章 實驗方法 42
3.1 實驗流程 42
3.2 試片製備 44
3.3 模擬沿海環境實驗設計 47
3.4 表面分析 49
3.5 成分分析 52
3.5.1 能量散佈Ｘ光分析儀(EDS) 52
3.5.2 光譜分析儀(OES) 53
3.5.3 感應耦合電漿光學發射光譜儀(ICP-OES) 53
3.6 深度分析 54
3.7 微硬度試驗 55
第四章 結果與討論 56
4.1 氯鹽沉積量 56
4.2 尚未進行腐蝕試驗的銲件表面形貌 57
4.3 微硬度量測結果 59
4.4 合成海鹽水溶液的實驗結果 60
4.4.1 U-bend銲件 60
4.4.1.1 腐蝕形貌 60
4.4.1.2 時間的影響 63
4.4.1.3 溫度的影響 67
4.4.1.4 孔蝕深度的量測 71
4.4.2 平板銲件 75
4.4.3 U-bend試片 78
4.4.4 平板試片 79
4.5 氯化鎂水溶液的實驗結果 81
4.5.1 U-bend銲件 81
4.5.1.1 腐蝕形貌 81
4.5.1.2 時間的影響 84
4.5.2 平板銲件 86
4.5.3 U-bend試片 88
4.5.4 平板試片 89
4.6 不同材料與試片類型結果比較 90
第五章 結論 92
第六章 未來建議方向 94
參考資料 95

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