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The Evaluation of Stress-Corrosion-Cracking and the Protection on 304l Stainless Steel with Salt-Crust Deposits(I)
|Contributors: ||NTOU:Institute of Materials Engineering|
|Issue Date: ||2011-06-28T07:09:28Z
|Abstract: ||摘要:沃斯田鐵系不銹鋼具有優良之耐蝕性及高經濟效能，因此一般核電廠廣泛使用沃斯田鐵系不銹鋼作為管路材料，並以銲接製程進行配管或組裝構件。此系列不銹鋼構件或管材於核電廠連續使用一段時間後，常在銲道及鄰近區域發生裂紋。一般認為沃斯 田鐵系不銹鋼因碳化鉻析出產生敏化現象，將導致腐蝕及應力腐 蝕破裂；此外，近年來多項研究結果顯示，銲接或機械加工現象， 尤其是大量冷加工後， 將引發鋼材之塑性變形， 是誘發不銹鋼發 生破裂之主要肇因。 已 知 介 穩 型 沃 斯 田 鐵 系 不 銹 鋼 如 AISI 304L 及316，會因塑性 變形而引發麻田散鐵變態， 而於使用過程中， 持續加熱將導致冷 加工之304L 不銹鋼，加速鉻碳化物大量析出，進而影響其耐蝕性 甚至應力破裂。核廢料乾式儲存用鋼槽，將採304L 不銹鋼經冷加 工及銲接成形後使用， 銲接及冷加工所導致的應力， 以及後續的 敏化現象， 恐導致此一設施在含氯鹽及濕氣腐蝕條件下引發鋼材 設施的劣化，因此，本研究工作主要針對304L 不銹鋼材，進行一 系列腐蝕劣化與防治之評估， 將以低濃度鹽霧模擬乾式儲存大氣 環境，評估測試沈積鹽層(Salt Crust)下，不銹鋼及其銲件試片應力 腐蝕龜裂行為與劣化速率， 建立乾式儲存用過核廢料密封不銹鋼 筒環境效應， 促進其完整性劣化之評估方法， 探討防治氯鹽誘發 不銹鋼應力腐蝕龜裂之最佳銲接程序與其他防治措施效益。此 外，建立完整的鹽霧應力腐蝕劣化機制，並評估最佳的防治對策， 進而提升不銹鋼材抗腐蝕劣化的能力及效益，亦是本研究之重點。|
abstract:Austenitic stainless steels(SSs) have been extensively applied to petrochemical and power industries because of their excellent general corrosion-resistance and low material cost. The line-pipe system in the nuclear power plant is constructed mainly using austenitic stainless steels (SSs) including AISI 304L and 316. Generally, arc welding processes are used to join the infrastructure and assembly those isolated components. After a period of service, cracks can be found in the regions near the weld metal. It is well known that the sensitization of SSs by forming chrominum-carbide precipitates is considered to deteriorate the corrosion resistance and enhance stress corrosion cracking (SCC). Furthermore, working numerous results reported recently that the residual stress induced by welding or machining especially cold working plays an important role in inducing cracking in SSs. Some commercial SSs, such as AISI 304L and 316 are metasatble and easy to transform to martensite steels during plastic deformation, typically caused by cold working in practical applications. Continuous heating also leads to enhance the stress corrosion cracking (SCC) of the cold-worked 304L by forming larger amounts of chromium carbides near grain boundary (so called sensitization). The applications of 304L in the Metal shielding in spent-fuel dry-interim storage facility is a typical example which the steel suffered severe cold-worked deformation and subjected to a welding procedure. It is very likely that mechanical cold-work and welding processes will induce residual stress, and result in sensitization of the steel, thereby leading to the degradation of SSs in NaCl-containing environments during industrial applications. Thus, the main goal of this proposal is to systemically study the SCC degradation and its prevention of 304L in the Metal shielding in spent-fuel dry-interim storage facility with salt-crust deposits. The mechanism of SCC and the degradation of alloy will also be explored, the entire evaluations and possible corrosion-prevention methods for the SCC of 304L will be proposed. It is of essence to wholly establish the corrosion mechanisms of 304L under SCC environments and the possible ways to enhance the corrosion resistance. The analyses of the phase constitutions after cold rolling and the effect of sensitization on the SCC susceptibility of the 304L stainless steel deposited with salt-crust are going to be performed in this study. The final goal of this research is not only to submit all results to be published in international journals but also to wholly establish the systematically high-performance database for the industrial applications.
|Appears in Collections:||[材料工程研究所] 研究計畫|
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