The effect of solidification micro constituents on the hot cracking susceptibility of Ni-based overlay weld

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Project title

Code/計畫編號

NL1070386

Translated Name/計畫中文名

鎳基合金覆銲組織熱裂性研究

Project Coordinator/計畫主持人

Leu-Wen Tsay

Funding Organization/主管機關

Atomic Energy Council

Department/Unit

Institude of Optoelectronic Sciences

Website

https://www.grb.gov.tw/search/planDetail?id=12583848

Year

2018

Start date/計畫起

01-05-2018

Expected Completion/計畫迄

31-12-2018

Bugetid/研究經費

620千元

ResearchField/研究領域

機械工程
材料科技

異質金屬銲接（Dissimilar Metal Welding）主要應用在鍋爐與過熱器、蒸氣管路等構件之銲接，然而異質金屬銲接由於異質母材間的物理性質差異，如熔點、熱膨脹係數及熱傳導係數，銲道之稀釋效應及填料選擇等因素，易造成異質金屬銲件的損壞及安全問題。國外核電廠在反應器壓力槽管嘴（低合金鋼）與冷卻水管件（不銹鋼）接口之鎳基合金銲道處，曾陸續發生應力腐蝕等破裂問題，為能有效防止裂痕的持續成長，除了採取管件的更換之外，另一替代方法為採用覆銲（Overlay）技術進行修補施作，即在銲道破裂處外表面施以覆銲層（Overlay weld），除了能增加管壁厚度外，亦可於管路內壁產生壓應力抑制裂縫成長，增強管路結構安全要求。此外，對於可能產生破裂之相關管件，核電廠亦採用預防性覆銲（Preemptive weld overlay，PWOL）技術預先進行修補，不但能避免銲道發生非預期破裂，亦可減少管路檢測作業提昇機組運轉效益。但鎳基合金覆銲層其沃斯田鐵組織具高熱裂敏感性，覆銲施銲參數不當（如熱輸入量過高），或覆銲基材含雜質含量偏高，皆會導致覆銲銲道發生熱裂。本研究係以氬銲（GTAW）多道次多重覆銲方式，使用鎳基合金IN 52M或IN 52MSS為填料進行覆銲製程，探討銲接熱輸入量、填料種類以及308L不銹鋼覆銲緩衝層等變因對鎳基覆銲層熱裂性影響，評估比較IN 52M及IN 52MSS鎳基填料之熱裂敏感性，並探討308L不銹鋼覆銲緩衝層，對減低鎳基合金覆銲層凝固邊界生成物之效益，瞭解308L不銹鋼緩衝層對改善鎳基合金覆銲層熱裂機制。 Recently stress corrosion cracks are found in dissimilar metal welds of some pressurized water reactor (PWR) in nuclear power plant. As a result, several mitigation methods have been applied to mitigate such cracks. The weld overlay has been applied to piping system in boiling water reactor components over some decades. Additionally, the weld overlay also provides other benefits including structural reinforcement and improved inspectability. In this study, stainless steel (308L) filler metal was employed to perform overlay welding on CF8A cast duplex stainless steels with different ferrite contents. The 308L was served as a buffer layer for the further overlay-welding of Ni-base alloy. Multi-passes gas tungsten arc welding (GTAW) is used for the overlay welding of this work. The microstructures in the HAZ of the CF8A substrate after multiple passes welding are examined, especially pays attention to the ferrite content and its morphology. Moreover, Gleebe thermal simulator will be used to generate the thermal cycles on the CF8A specimens with distinct ferrite contents, which may take place during overlay-welding. Moreover, the SCC susceptibility of such overlay welds was evaluated by using a modified smooth tensile specimen, which was strained at constant extension rate tensile (CERT) tests under simulated coolant conditions in a nuclear reactor. The percentage loss in tensile strength and ductility of various specimens in high-temperature water due to SCC could be calculated accordingly.

Keyword(s)

鎳基合金
異質金屬銲接
覆銲
Ni-base alloy
Dissimilar Metal Welding
Overlay

DSpace CRIS

The effect of solidification micro constituents on the hot cracking susceptibility of Ni-based overlay weld

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