近數十年來，隨著全世界核能發電廠的運轉時間增長，沸水式反應器已發現許多材料劣化的現象。目前已有許多關於反應器內部的組件材料遭受沿晶應力腐蝕(Intergranular Stress Corrosion Cracking, IGSCC)的案例。應力腐蝕龜裂的三大要素為敏感性材料、腐蝕性環境與張應力。如何去除或減少應力腐蝕龜裂三大要素的影響便是相當重要的課題，藉由熱處理降低材料敏感性、施行加氫水化學(Hydrogen Water Chemistry , HWC)與消除殘留應力皆為可行之方法。其中加氫水化學能使得水環境之氧化性降低，進而降低材料之電化學腐蝕電位(Electrochemical corrosion potential, ECP)，減緩腐蝕的發生。本實驗的材料為316L不鏽鋼與鎳基52合金之異質銲接材料，對銲接後之材料執行硬度測試、殘留應力測試與不同溫度的熱處理，評估氬銲對銲材52合金與母材316L不鏽鋼之影響，觀察銲道、熱影響區與基材之微結構。不同溫度的熱處理下的異材銲件應力腐蝕龜裂是本研究討論的重點之一。
本實驗為在模擬沸水式反應器之高溫高壓純水中，進行慢應變速率拉伸試驗(Slow Strain Rate Testing , SSRT)，從應力應變曲線來評估材料之機械性質；拉伸破斷後之試棒，以掃描式電子顯微鏡觀察材料之破斷面形貌，討論不同形貌表現所對應之破裂機制，進而評估最適當之材料處理方法。結果顯示，銲接後熱影響區與遠離熱影響區母材之金相微結構差異甚小，所有試棒皆斷裂於遠離熱影響區之316L不鏽鋼母材。在溶氫與溶氧環境中，材料經過固溶退火熱處理後有較好的機械性質，而不鏽鋼的銲後熱處理則使其傾向產生應力腐蝕龜裂。而加氫水化學條件下，應力腐蝕龜裂的敏感性能被明顯抑制。總體而言，固溶熱處理與加氫水化學能有效抑制材料之腐蝕敏感性，而固溶熱處理與未熱處理試棒的抗應力腐蝕龜裂能力皆優於銲後熱處理條件之表現。

There have been a great number of occurrences of stress corrosion cracking (SCC) in the structural materials of boiling water reactors (BWRs) in recent decades. Stress corrosion cracking consists of three main factors: susceptible materials, caustic environments and tensile stress. To address this crucial issue, researches have been investigating the effect of these three factors for decades. Reducing the susceptibility of the materials by heat treatments, applying hydrogen water chemistry (HWC) and eliminating residual stress are several feasible methods. The water environments became less oxidizing after applying HWC, which lowered the electrochemical corrosion potential (ECP) and thus mitigated stress corrosion cracking. In this study, 316L SS and alloy 52 were used in the dissimilar metal weld (DMW). Hardness and residual stress measurements on the surface of the DMW as well as heat treatments were performed after tungsten inert gas (TIG) welding. The effect of welding on the microstructure of the weld, heat affected zone and unaffected base metal was also evaluated. The influence of heat treatments with different temperatures on SCC was also investigated.
In this study, slow strain rate testing (SSRT) was implemented in simulated BWR water environments. The mechanical properties of the materials were determined from the stress-strain curve, and the fracture surfaces were characterized via scanning electron microscope (SEM). From the above steps, we evaluated the most effective way to mitigate SCC. The results showed that the difference in microstructure between heat affected and unaffected zone was insignificant. All samples were fractured at the base metal 316L SS, which was distant from the heat affected zone. In dissolved oxygen and dissolved hydrogen environments, the materials exhibited higher mechanical ductility after solution annealing. But the materials tended to be susceptible to stress corrosion cracking after post weld heat treatment. On the whole, solution annealing treatment and HWC could remarkably lower the susceptibility of the materials. As-welded samples exhibited lower susceptibility to SCC than samples with one post weld heat treatment.

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